BBC foreign correspondent Jon Leyne has died in London at the age of 55.
One of the BBC's most experienced journalists, Leyne covered wars and unrest in many regions over the past three decades.
He joined the BBC in 1985, and worked as UN correspondent in the early 1990s before serving around Europe and the Middle East, as well as in Washington.
In recent years, Leyne covered the Libyan uprising against Col Muammar Gaddafi and the Egyptian revolution.
Acting Director BBC News Fran Unsworth said: "Jon was a brave and courageous journalist in the best traditions of the BBC. He had an insatiable curiosity and told complex stories in an engaging and accessible way."
Iran posting
In 2001, Leyne was US state department correspondent and close to the Pentagon when the building was attacked from the air on 11 September.
In the following years he travelled the world covering the journeys of then-Secretary of State Colin Powell.
Leyne was appointed correspondent in Jordan and covered the 2006 conflict between Israel and Lebanese militant group Hezbollah.
While working in Iran during the 2009 elections, he was asked to leave within 24 hours by the Tehran authorities who accused Britain and the BBC of meddling in internal affairs.
Earlier this year, he ended his Cairo posting early after suffering from severe headaches.
He returned to Britain for treatment and was diagnosed with an incurable brain tumour.
The driver of a train that derailed in Spain killing 78 people has been accused of "reckless manslaughter", the interior minister has said.
Jorge Fernandez Diaz said Francisco Jose Garzon Amo, who was slightly hurt in Wednesday's accident, had been taken to a police station.
Mr Garzon is suspected of driving too fast on a bend. Reports say the train was travelling at more than double the speed limit at the time of the crash.
He has refused to answer questions.
At least 130 people were taken to hospital after the accident near the north-western city of Santiago de Compostela.
Thirty were in a critical condition on Saturday.
The last carriage is removed from the scene of the derailment
People from several nationalities were among the wounded, including five Americans and one Briton. One American was among the dead.
PM Mariano Rajoy, who hails from the city of the crash, declared three days of official mourning on Thursday.
All but three of the 78 people killed have now been identified, the BBC's Alison Roberts reports.
Investigators have been forced to use DNA matches because of the extent of the injuries, our correspondent adds.
Experienced driver
A judge was due to interview Mr Garzon Amo on Sunday, the interior minister said.
Video posted online appears to show the moment the train derailed, from the trackside
"He has been detained for the alleged crimes of reckless manslaughter", Mr Fernandez Diaz said.
"There are reasonable grounds to consider that he may have been responsible for what happened, which must be established by a judge and the investigation."
The driver had been under police surveillance in hospital since the accident but he was discharged on Saturday and taken to a police station.
Police said Mr Garzon Amo had refused to answer their questions while he was in medical care.
State rail operator Renfe said the train came off the tracks about 3 or 4km (2-2.5 miles) from Santiago de Compostela station at 20:41 local time (18:41 GMT) on Wednesday.
The accident occurred on the express route between the capital, Madrid, and the port city of Ferrol on the Galician coast, with 218 passengers on board and four crew members.
Footage captured by a security camera shows the train crashing as it hurtled round a bend.
The train's data recording "black box" is with the judge in charge of the investigation.
Renfe president Julio Gomez Pomar was quoted by El Mundo newspaper as saying the 52-year-old driver had 30 years of experience with the company and had been operating trains on the line for more than a year.
Mr Pomar said the train had no technical problems.
The derailment happened on the eve of Santiago de Compostela's main annual festival where thousands of Christian pilgrims were expected to flock to the city in honour of St James.
The local tourism board cancelled all festivities as the city went into mourning.
Some trains have now begun running on the tracks despite some passengers' hesitation, our correspondent says.
According to official figures, the crash is one of the worst rail disasters in Spanish history.
27 July 2013Last updated at 11:52 ETBy Keith MooreBBC News
A petition calling on Twitter to add a "report abuse" button has received thousands of signatures.
It follows a deluge of abuse and rape threats received by Caroline Criado-Perez, who successfully campaigned for women to be included on UK banknotes.
MP Stella Creasy told the BBC she was "furious" Twitter had yet to do anything about Ms Criado-Perez's abuse.
Twitter UK's Tony Wang later said the company was "testing ways to simplify" reporting abuse.
'Frequently ignored'
Ms Criado-Perez, who had appeared in the media to campaign for women to feature on banknotes, said the abusive tweets began the day it was announced that author Jane Austen would appear on the newly designed £10 note.
She reported them to the police after receiving "about 50 abusive tweets an hour for about 12 hours" and said she had "stumbled into a nest of men who co-ordinate attacks on women".
Once again, a social network is at the centre of a storm over hateful and offensive content posted by its own users.
Twitter now faces a tricky dilemma - it has never been keen to police the messages posted by its users, and wants to be seen as a protector of free speech.
If it agrees to campaigners' demands for a "report abuse" button on every tweet, it will then need to employ an army of monitors to respond to complaints and decide what constitutes abuse.
The company would prefer that threatening tweets were referred to the police, who in the UK have been active in pursuing social media users suspected of breaking the law.
But with a campaign for a boycott on 4 August gathering pace, Twitter will need to show it understands the pressure to make the network a safer and more polite place - and come up with ideas to make that happen.
Ms Criado-Perez, from Rutland, told the BBC she had also tried to contact Twitter's manager of journalism and news, Mark Luckie, about the rape threats she was receiving, but he did not respond and locked his tweets to become private.
She said the form that allows Twitter users to report abuse was not adequate - particularly when such a high volume of abuse was being received. "Twitter need to be on the side of the victims," she said.
An online petition has been started in response to the abuse Ms Criado-Perez received calling for Twitter to introduce a "report abuse" button. It had been signed by more than 9,000 people by 15:00 BST on Saturday.
Kim Graham from Great Yarmouth, Norfolk, put the petition online at 09:00 BST after seeing abuse that Ms Criado-Perez had been getting. She told the BBC the "report abuse" button was something that came into her mind after finding it was "harder than it should be to report abuse".
The petition says: "Abuse on Twitter is common; sadly too common. And it frequently goes ignored. We need Twitter to recognise that its current reporting system is below required standards.
"The report abuse button needs to be accompanied by Twitter reviewing the T&C [terms and conditions] on abusive behaviour to reflect an awareness of the complexity of violence against women, and the multiple oppressions women face. It's time Twitter started protecting its users."
'Hate crime'
Ms Criado-Perez's cause has been supported by other prominent tweeters, including the journalists Caitlin Moran and Suzanne Moore and Independent columnist Owen Jones.
Ms Moran has called for a 24-hour Twitter boycott on 4 August to try to get Twitter to come up with an "anti-troll policy".
Labour MP Ms Creasy said: "This is not a technology crime - this is a hate crime. If they were doing it on the street, the police would act."
She told the BBC she had been chasing Twitter for the past 24 hours but they had not yet responded to her.
"I am absolutely furious with Twitter that they are not engaging in this at all," she said.
A Twitter spokesperson said: "We don't comment on individual accounts. However, we have rules which people agree to abide by when they sign up to Twitter. We will suspend accounts that once reported to us, are found to be in breach of our rules.
"We encourage users to report an account for violation of the Twitter rules by using one of our report forms."
The general manager of Twitter UK, Tony Wang, later tweeted that the company was "testing ways to simplify reporting, e.g. within a Tweet by using the 'Report Tweet' button in our iPhone app and on mobile web".
A Metropolitan Police spokesman confirmed that "officers from Camden have received an allegation regarding comments made via a social network, that was reported on 25 July".
He added that "inquiries continue" but so far there had been "no arrests".
There have been some high profile arrests related to celebrities abused on Twitter, including a teenager arrested over the abuse of Great Britain's Olympic diver Tom Daley.
Guidelines published by the Director of Public Prosecutions Keir Starmer in June said there should be a "high threshold for prosecution in cases involving communications which may be considered grossly offensive, indecent, obscene or false".
25 July 2013Last updated at 15:28 ETBy Melissa HogenboomScience reporter, BBC News
False memories have been implanted into mice, scientists say.
A team was able to make the mice wrongly associate a benign environment with a previous unpleasant experience from different surroundings.
The researchers conditioned a network of neurons to respond to light, making the mice recall the unpleasant environment.
Reporting in Science, they say it could one day shed light into how false memories occur in humans.
The brains of genetically engineered mice were implanted with optic fibres in order to deliver pulses of light to their brain. Known as optogenetics, this technique is able to make individual neurons respond to light.
Our memory changes every single time it's being recorded. That's why we can incorporate new information into old memories and this is how a false memory can form..."
End QuoteDr Xu LiuMassachusetts Institute of Technology
Just like in mice, our memories are stored in collections of cells, and when events are recalled we reconstruct parts of these cells - almost like re-assembling small pieces of a puzzle.
It has been well documented that human memory is highly unreliable, first highlighted by a study on eyewitness testimonies in the 70s. Simple changes in how a question was asked could influence the memory a witness had of an event such as a car crash.
When this was brought to public attention, eyewitness testimonies alone were no longer used as evidence in court. Many people wrongly convicted on memory statements were later exonerated by DNA evidence.
Xu Liu of the RIKEN-MIT Center for Neural Circuit Genetics and one the lead authors of the study, said that when mice recalled a false memory, it was indistinguishable from the real memory in the way it drove a fear response in the memory forming cells of a mouse's brain.
The mouse is the closest animal scientists can easily use to analyse the brain, as though simpler, its structure and basic circuitry is very similar to the human brain.
Studying neurons in a mouse's brain could therefore help scientists further understand how similar structures in the human brain work.
"In the English language there are only 26 letters, but the combinations of letters make unlimited words and sentences, this is also true for memories," Dr Liu told BBC News.
Evolving memories
"There are so many brain cells and for each individual memory, different combinations of small populations of cells are activated."
These differing combinations of cells could partly explain why memories are not static like a photograph, but constantly evolving, he added.
Mice have previously been trained to believe they were somewhere else, "a bit like the feeling of deja-vu we sometimes get", said Rosamund Langston from Dundee University.
A possibility in the future is erasing memories, she told BBC News.
"Episodic memories - such as those for traumatic experiences - are distributed in neurons throughout the brain, and in order to make memory erasure a safe and useful tool, we must understand how the different components of each memory are put together.
"You may want to erase someone's memory for a traumatic event that happened in their home, but you certainly do not want to erase their memory for how to find their way around their home."
"If you want to grab a specific memory you have to get down into the cell level. Every time we think we remember something, we could also be making changes to that memory - sometimes we realise sometimes we don't," Dr Liu explained.
"Our memory changes every single time it's being 'recorded'. That's why we can incorporate new information into old memories and this is how a false memory can form without us realising it."
Susumu Tonegawa, also from RIKEN-MIT, said his teams' work provided the first animal model in which false and genuine memories could be investigated in the cells which store memories, called engram-bearing cells.
"Humans are highly imaginative animals. Just like our mice, an aversive or appetitive event could be associated with a past experience one may happen to have in mind at that moment, hence a false memory is formed."
Silencing fear
Neil Burgess from University College London, who was not involved with the work, told BBC News the study was an "impressive example" of creating a fearful response in an environment where nothing fearful happened.
"One day this type of knowledge may help scientists to understand how to remove or reduce the fearful associations experienced by people with conditions like post traumatic stress disorder."
But he added that it's only an advance in "basic neuroscience" and that these methods could not be directly applied to humans for many years.
"But basic science always helps in the end, and it may be possible, one day, to use similar techniques to silence neurons causing the association to fear."
'Diseases of thought'
Mark Mayford of the Scripps Research Institute in San Diego, US, said: "The question is, how does the brain change with experience? That's the heart of everything the brain does.
He explained that work like this could one day further help us to understand the structure of our thoughts and the cells involved.
"Then one can begin to look at those brain circuits, see how they change, and hopefully find the areas or mechanisms that change with learning."
"The implications are potentially interventions for diseases of thought such as schizophrenia. You cannot approach schizophrenia unless you know how a perception is put together."
More than 100 people have been killed and 1,500 injured at a protest held by supporters of ousted Egyptian President Mohammed Morsi in Cairo, doctors say.
However the health ministry has put the death toll lower, at 38.
The army ousted Mr Morsi on 3 July. He has been formally accused of murder, relating to a 2011 jail outbreak, and of links to the militant group Hamas.
Both pro- and anti-Morsi demonstrators held huge protests overnight in the capital.
There were pools of blood all over the field hospital. Many of the injured were in bad shape. Some had parts of their head missing - taken out by bullets.
The battle raged last night and all morning. We heard automatic gunfire. Protesters formed a human shield around us as shotguns and CS gas were fired towards us. There was the sound of outgoing shots too. The air was thick with tear gas and people were vomiting.
There was a child, maybe 12, covered in blood. He was deathly white. They closed the doors at the hospital as they could not accept more wounded, but the ambulances were still arriving.
As we left, a child was dragged from a car by the Morsi supporters outside the mosque. He was given a very serious beating.
The anti-Morsi camp occupied Cairo's Tahrir Square in support of the army, after its chief, Gen Abdel Fattah al-Sisi, had urged people to demonstrate to provide a mandate for its intervention.
Meanwhile, tens of thousands of Morsi supporters continued their sit-in protest at the mosque in the Nasr City area.
On Saturday, Interior Minister Mohammed Ibrahim vowed to end the sit-in, saying local residents had complained about the encampment.
He said the protest would be "brought to an end soon, and in a legal manner" with an order from the prosecutor, although this has yet to happen.
The BBC's Jim Muir in Cairo says the latest violence is the most serious since the army's intervention to remove President Morsi, but this does not appear to have been a planned campaign to clear the area around the mosque.
'Shooting to kill'
It appears that clashes began after some of the Morsi supporters tried to block a main road in the area, and security forces responded.
The state news agency Mena quotes a security official as saying they had been trying to stop fighting between rival sides, and that eight security personnel had been injured.
The official added that live fire had not been used, only tear gas.
Muslim Brotherhood's spokesperson says the international community must step in
But our correspondent says medics at the hospital believed about 70% of the casualties were caused by live fire - with many of the victims hit in the chest or head by snipers firing from rooftops.
Ahmed Nashar, a Brotherhood spokesman witnessed what happened near the Nasr City mosque where demonstrators built a wall to protect themselves.
"When I arrived, bullets were whizzing past my ears," he told the BBC. "Today was just brutal - people were fired at, with live firearms."
Our correspondent says Morsi supporters are furious about the role the military is taking, and in particular the head of the army, General Abdel Fattah al-Sisi, whom they say is killing Egyptians.
Egypt's pro-Muslim Brotherhood TV station, Ahrar 25, quoted the coalition that supports Mr Morsi - the National Coalition for Supporting Legitimacy - as saying it held Gen Sisi responsible for the deaths at the mosque protest.
There has also been violence in Egypt's second city of Alexandria, where at least 10 people have been killed in clashes between rival factions.
European Union foreign policy chief Catherine Ashton said she "deeply deplored" the latest deaths in Egypt.
Dr Hesham Ibrahim described scenes at the hospital as like "hell"
Her spokesman called "on all actors to refrain from violence and to respect the principles of peaceful protest".
UK Foreign Secretary William Hague said: "Now is the time for dialogue, not confrontation. It is the responsibility of leaders on all sides to take steps to reduce tensions."
Morsi accused
Mr Morsi, Egypt's first democratically elected president, has been formally remanded in custody at an undisclosed location for an initial 15-day period, according to a judicial order on Friday.
The order was the first official statement on Mr Morsi's legal status since he was overthrown.
He has now been formally accused of the "premeditated murder of some prisoners, officers and soldiers" when he and several Muslim Brotherhood leaders were freed during a breakout at a Cairo prison in January 2011.
He is alleged to have plotted attacks on jails in the uprising that overthrew President Hosni Mubarak.
Mr Morsi is also accused of conspiring with the Palestinian militant group Hamas, which governs the Gaza Strip and has strong links with the Muslim Brotherhood.
Two human rights activists visited Mr Morsi's place of detention on Friday, although he reportedly refused to meet them, instead sending his chief of presidential staff Refaa el-Tahtawy - who is also held at the location.
Mr Tahtawy told the visitors they were being treated well but complained that they were unable to meet relatives.
On Saturday, the interior minister Ibrahim said that Mr Morsi would be transferred to Torah Prison, where Mubarak is being held.
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The top US military officer has outlined the costs, risks and benefits of possible American military involvement in the Syrian conflict.
Joint Chiefs of Staff chairman Gen Martin Dempsey offered five military options, including limited strikes and establishing a no-fly zone.
But he said using force in Syria would be "no less than an act of war" and could cost the US billions of dollars.
Washington has so far ruled out military intervention in Syria.
Its role in the conflict is currently limited to delivering humanitarian aid to Syrian refugees in neighbouring countries and providing non-lethal help to the Syrian opposition.
'Act of war'
In an open letter to senators, Gen Dempsey analysed five military options the US military could potentially undertake in Syria:
training, advising and assisting the opposition
conducting limited strikes
establishing a no-fly zone
creating buffer zones inside Syria
controlling Damascus' chemical arms
Gen Dempsey estimated that the first option would cost about $500m (£325m) a year, while each of the other four actions would require roughly $1bn a month.
"The decision to use force is not one that any of us takes lightly. It is no less than an act of war," he wrote in the letter.
Gen Dempsey acknowledged that the outlined actions would strengthen the opposition and put more pressure on President Bashar al-Assad, but he warned the US should learn from its previous interventions, as in Afghanistan and Iraq.
"We have learned from the past 10 years, however, that it is not enough to simply alter the balance of military power without careful consideration of what is necessary in order to preserve a functioning state," he said.
Gen Dempsey's letter was in response to questions by two members of the Senate Armed Services Committee which is considering re-appointing him for a second two-year term as chairman of the joint chiefs.
More than 90,000 people have been killed in Syria since the uprising again President Assad began in 2011, according to the UN.
A further 1.7 million have been forced to seek shelter in neighbouring countries.
Storms have hit England and Wales with warnings of more to come following the UK's hottest day since July 2006.
London, Kent, Essex, Cambridgeshire and the Midlands are among places affected. In Market Bosworth, Leicestershire, 21mm of rain fell in less than an hour, the BBC Weather Centre said.
The Met Office's Yellow warning for Tuesday predicts "thunderstorms or longer spells of thundery rain during the course of Tuesday, with some torrential downpours in places".
It also warns of "the risk of localised disruption to travel" and "surface water flooding".
In Wales, Natural Resources Wales said heavy rain was likely to cause roads to flood and drains, ditches and small streams to overflow.
A further yellow warning of rain has been issued for Wednesday, affecting eastern parts of England and parts of Scotland, in particular the north-east of the country.
The BBC Weather Centre said that, on Wednesday, the focus of the storms would move away from Wales and south-west England with Scotland increasingly at risk into the early hours of Wednesday morning.
Prolonged heatwave
Earlier on Monday night, BBC forecasters said the night ahead could get "very close" to breaking the UK record for the highest overnight minimum temperature.
The existing highest minimum was set one night in Brighton in August 1990, when the temperature did not fall below 23.9C (75F).
Forecasters said that record could fall somewhere west or south-west of London.
As for the seven-year-high daytime reading of 33.5C - recorded at Heathrow and Northolt on Monday - that may be revised upwards as the BBC Weather Centre said delayed reports from smaller weather stations could produce a higher reading.
Dr Vincent Janik, from the university's Sea Mammal Research Unit, said: "(Dolphins) live in this three-dimensional environment, offshore without any kind of landmarks and they need to stay together as a group.
"These animals live in an environment where they need a very efficient system to stay in touch."
Signature whistles
It had been-long suspected that dolphins use distinctive whistles in much the same way that humans use names.
Previous research found that these calls were used frequently, and dolphins in the same groups were able to learn and copy the unusual sounds.
But this is the first time that the animals response to being addressed by their "name" has been studied.
Most of the time they can't see each other, they can't use smell underwater... and they also don't tend to hang out in one spot"
End QuoteDr Vincent JanikUniversity of St Andrews
To investigate, researchers recorded a group of wild bottlenose dolphins, capturing each animal's signature sound.
They then played these calls back using underwater speakers.
"We played signature whistles of animals in the group, we also played other whistles in their repertoire and then signature whistles of different populations - animals they had never seen in their lives," explained Dr Janik.
The researchers found that individuals only responded to their own calls, by sounding their whistle back.
The team believes the dolphins are acting like humans: when they hear their name, they answer.
Dr Janik said this skill probably came about to help the animals to stick together in a group in their vast underwater habitat.
He said: "Most of the time they can't see each other, they can't use smell underwater, which is a very important sense in mammals for recognition, and they also don't tend to hang out in one spot, so they don't have nests or burrows that they return to."
The researchers believe this is the first time this has been seen in an animal, although other studies have suggested some species of parrot may use sounds to label others in their group.
Dr Janik said that understanding how this skill evolved in parallel very different groups of animals could tell us more about how communication developed in humans.
A Norwegian woman at the centre of a Dubai rape case dispute has been pardoned and is free to leave Dubai, she has said.
Interior designer Marte Deborah Dalelv, 24, was on a business trip in Dubai when she says she was raped in March.
She reported the attack to the police, but was charged with perjury, having extramarital sex and drinking alcohol, receiving a 16-month prison sentence.
The case has angered rights groups and the Norwegian authorities.
The fact Ms Dalelv's pardon came within days of an international outcry - and was reportedly ordered personally by Dubai's ruler - is a recognition of how badly this case has reflected on the Gulf state.
This is an emirate that doesn't have much oil - instead, tourism is at the centre of its economy. It clocked up 10 million visitors last year and wants to double that by 2020.
And while it sticks by the strict Islamic laws that govern the UAE, Dubai knows that these negative headlines do it no favours. It will be hoping this swift action will limit the damage to its reputation.
But the pardoning of Ms Dalelv's alleged rapist as part of the deal which allows her to return to Norway - is already causing a backlash on social media.
Ms Dalelv has had her passport returned and was free to leave the country, a Norwegian official told the BBC. She was not being deported, and was expected to return to Norway in the next few days.
The designer, who has been staying at the Norwegian Seamen's Centre in Dubai since she was sentenced last week, told the BBC she found out she was to be freed earlier on Monday during a meeting with public prosecutors.
"We came in and we sat down and they told us 'You've been pardoned'. It's from the ruler of Dubai. It's from him personally so that's - it just feels unbelievable - it's a very, very good day."
Her travel documents had now been returned to her and she was preparing to leave Dubai as soon as possible, Ms Dalelv said.
In Norway, Foreign Minister Espen Barth Eide tweeted: "Marte is released! Thanks to everyone who signed up to help."
The Norwegian government said it had been in daily contact with the Dubai authorities through diplomatic and official channels since Ms Dalelv was sentenced - arguing the jail term represented a human rights violation.
Ms Dalelv went public about the sentence last week in a series of interviews.
Night out
Ms Dalelv says she was on a night out with colleagues on 6 March when the rape took place.
She reported it to the police, who proceeded to confiscate her passport and seize her money. She was charged four days later on three counts, including having sex outside marriage.
Her alleged attacker, she said, received a 13-month sentence for extramarital sex and alcohol consumption.
The man she accused of raping her - a colleague - has also been pardoned, a Norwegian official has said.
Despite developing fast as a cosmopolitan tourism destination in recent years, Dubai remains deeply conservative, and its strict laws have caught out foreigners in the past.
Public displays of affection and drunkenness are frowned upon.
Chinese state television shows the moment the earthquake struck Dingxi
Two powerful earthquakes have struck China's north-west Gansu province, killing at least 75 people and leaving more than 400 others injured.
The first earthquake near Dingxi city had a magnitude of 5.98 and was shallow, with a depth of just 9.8 km (6 miles), the US Geological Survey said.
Just over an hour later, a magnitude 5.6 quake hit the same area, it added.
In 2008, an earthquake in Sichuan province left up to 90,000 people dead and millions homeless.
A factory worker in Minxian county told AFP that he felt "violent shaking" and "ran to the yard of the [factory] plant immediately".
"Our factory is only one floor. When I came to the yard, I saw an 18-storey building, the tallest in our county, shaking ferociously, especially the 18th floor," he said.
The area has been hit by 371 aftershocks, according to the Earthquake Administration of Gansu province.
Tremors were felt in the provincial capital, Lanzhou, and as far away as Xian, 400km (250 miles) to the east.
At least 5,600 houses in the province's Zhangxian county are seriously damaged and 380 have collapsed, while some areas suffered from power cuts or mobile communications being disrupted, the earthquake administration added.
"Many have been injured by collapsed houses," a doctor based in Minxian county was quoted by Reuters news agency as saying. "Many villagers have gone to local hospitals along the roads."
The earthquake has caused a direct economic loss of 198 million yuan ($32m; £21m), the Dingxi government said on its microblog.
'Vibrating'
Both the Chinese President Xi Jinping and Premier Li Keqiang had called Gansu province to express their concern for the victims and stress the importance of the rescue operations being conducted well, the Dingxi government added.
Crews of fire fighters and rescue dogs have already arrived at the scene, the BBC's Celia Hatton in Beijing reports.
The closer to the surface an earthquake strikes, the more damage it can cause, our correspondent adds.
The earthquake reportedly triggered a series of mudslides and landslides, making it difficult for rescuers to access some areas hit by the quake.
The Gansu military police have deployed 500 soldiers, including 120 specialist rescuers, while 500 emergency tents and 2,000 quilts are also being transported to affected areas, Xinhua added.
Officials from the civil affairs, transportation and earthquake departments were also visiting local towns to assess the damage, a statement on the Dingxi party website said.
Rain is expected in the region later, leading to fears that this will make rescue efforts more difficult, or cause more landslides.
"Showery weather is expected tomorrow, and lighter rain the day after that. The rain may have an adverse effect on rescue efforts - please pay attention and be on guard!" the Dingxi government wrote on its microblog.
Residents in towns near the earthquake also reported feeling the tremors.
"You could see the chandeliers wobble and the windows vibrating and making noise, but there aren't any cracks in the walls," AP news agency quoted a clerk at Wuyang Hotel, about 40 km (25 miles) from the epicentre, as saying.
"Shop assistants all poured out onto the streets when the shaking began," the clerk said.
A flaw with mobile phones' Sim card technology is putting millions of people at risk of being spied on and robbed, according to a leading security expert.
Karsten Nohl has said he has found a way to discover some Sims' digital keys by sending them a special text message.
He warned criminals could potentially use the technique to listen in on calls or steal cash.
Industry organisation - the GSMA - said it was looking into the findings.
"Karsten's early disclosure to the GSMA has given us an opportunity for preliminary analysis," said a spokeswoman for the association, which represents global network operators,
"We have been able to consider the implications and provide guidance to those network operators and Sim vendors that may be impacted.
"It would appear that a minority of Sims produced against older standards could be vulnerable."
Mr Nohl has posted preliminary details of the vulnerability on the website of his company, Berlin-based Security Research Labs.
Intercepted calls
Sim (subscriber identity module) cards effectively act as a security token, authenticating a user's identity with their network operator.
They also store a limited amount of data such as text messages, contacts' telephone numbers and details used for some applications - including a number of payment and banking services.
Mr Nohl said he had found a way to discover the authentication code by sending a device a text message masquerading as a communication from the user's mobile operator.
The message contained a bogus digital signature for the network.
He said most phones cut contact after recognising the signature as being a fake - but in about a quarter of cases, the handsets sent back an error message including an encrypted version of the Sim's authentication code.
The encryption is supposed to prevent the authentication code being discovered, but Mr Nohl said that in about half of these cases it was based on a 1970s coding system called Digital Encryption Standard (DES), which was once thought secure but could now be cracked "within two minutes on a standard computer".
Once the attacker had this information, Mr Nohl said, they could download malware to the Sim written in the Java programming language.
He said these could be used by the hacker to send texts from the device to premium rate numbers they had set up, to discover and listen in to the target's voicemail messages and to track their location.
In addition, he warned that combined with other techniques, it could act as a surveillance tool.
"Sim cards generate all the keys you use to encrypt your calls, your SMS and your internet traffic," Mr Nohl told the BBC.
"If someone can capture the encrypted data plus have access to your Sim card, they can decrypt it.
"Operators often argue that it's not possible to listen in on 3G or 4G calls - now with access to the Sim card, it very much is."
Mr Nohl said that his research suggested about an eighth of all Sim cards were vulnerable to the hack attack - representing between 500 million to 750 million devices.
Although Mr Nohl would not reveal at this time in which countries DES encryption remained most common, he did say that Africa-based users had particular cause for concern.
"Here in Europe we use a Sim card to make phone calls and texts, but many people in Africa also use them for mobile banking," he said.
"Someone can steal their entire bank account by copying their Sim card.
"That adds a certain urgency because you imagine fraudsters would be most interested in breaking into their Sim cards - especially when it can be done remotely."
Black Hat
Mr Nohl said he expected network operators would not take long to act on his study, and should be able to provide an over-the-air download to protect subscribers against the vulnerability.
The GSMA said that it had not yet seen the full details of his research, but planned to study it to pinpoint any issues that could be fixed.
It added that "there is no evidence to suggest that today's more secure Sims, which are used to support a range of advanced services, will be affected".
The UN's telecoms agency - the International Telecommunications Union - said that it would now contact regulators and other government agencies worldwide to ensure they were aware of the threat.
Mr Nohl said he planned planned to reveal more information about the vulnerability at the Black Hat security conference in Las Vegas later this month.
However, he said he would not publish a survey showing which phone owners were most at risk until December to give operators an opportunity to address the problem.
22 July 2013Last updated at 21:39 ETBy Nick BryantBBC News, New York
Americans began July celebrating their independence from colonial rule. Less than three weeks later, many are rejoicing at the birth of a royal baby boy.
It is one of the great American paradoxes that a country which got rid of the monarchy in 1776 continues to lavish so much attention on the Royal Family.
One thing that the Windsors continue to command here is airtime on American television and column inches in the newspapers.
There has been blanket coverage on the rolling news channels. Websites such as the New York Post have redesigned their front pages to accommodate the breaking news.
News shows have also been heavily populated by plummy-voiced "royal watchers". For its rolling coverage, CNN bagged the British ambassador in Washington, Sir Peter Westmacott, who appeared resplendent in a red, white and blue tie.
'Stuffy protocols'
That news channel also replaced its normal jingles with regal-sounding music. Needless to say, the birth announcement has led all the network bulletins.
New Yorkers 'thrilled' by royal baby
Like CNN, ABC News replaced the thumping beat of its usual news anthem with dainty strings. One half-expected the news anchor, Diane Sawyer, to appear in period costume.
For weeks now, as the "great Kate wait" continued, the US media has covered the story from all manner of angles. The website The Daily Beast has focused on the possible stimulus effect of the birth on "austerity Britain."
National Public Radio was intrigued on what surname the new baby would have.
The New York Times, adopting a more sceptical tone, has tried to make sense of the "stuffy protocols" surrounding royal events, treating them as a throwback or museum piece.
For the New York Times, the royal easel erected on the forecourt of Buckingham Palace became an object of great fascination.
I was in Times Square in the heart of New York City when the news started coming through, which soon flashed up on the big screen news tickers.
Some people could hardly contain their delight. One woman screamed: "Oh my god. Oh, great, alright!"
Another said: "Oh congratulations, Kate, that's awesome."
Others could not really care less.
'Diana effect'
In a corner of Greenwich Village sometimes known as Little Britain, a restaurant catering for those with the taste for the United Kingdom hung up union flag bunting and "It's a Boy" celebratory banners. Champagne was sipped from bone-china teacups.
President Barack Obama and his wife, Michelle, were quick to send their congratulations to the royal couple on the occasion.
"We wish them all the happiness and blessings parenthood brings," they said.
"Given the special relationship between us, the American people are pleased to join with the people of the United Kingdom as they celebrate the birth of the young prince."
Of course, that special relationship, that connection between Britain and America, explains much of the wall-to-wall coverage.
And US historians will tell you that the fascination with the royals is nothing new. The coronation of Queen Victoria, for instance, was one of the great news events of its day.
What is new is the marriage of British regal tradition with American celebrity culture - a union which came to be crystallised in 1985 when Princess Diana danced with John Travolta at a White House state dinner.
Princess Diana became Vanity Fair magazine's favourite cover girl. Her death was as much an emotional event for many Americans as it was for grieving Britons.
Hollywood A-list
Tellingly, much of the coverage has focused on the absence of Diana. "What about the grandmother they will never meet?" asked ABC news anchor Diane Sawyer, wistfully.
To this day the two princes, William and Harry, remain beneficiaries of the "Diana effect".
When Harry toured America in May he was greeted with what the local media called "Harrymania".
The Duchess of Cambridge is also a hugely popular figure here, and has become a fashion icon.
They have become A-list celebrities in the US cultural hierarchy, with the star power to eclipse even Hollywood's biggest names.
As the American reaction to the royal birth reminds us, the royals have become an offshoot of the US entertainment industry.
This royal birth also serves as another reminder of America's umbilical link with Britain.
A formal bulletin confirming the birth was displayed at Buckingham Palace
Thousands of well-wishers descended on Buckingham Palace on Monday night to celebrate the birth of the Duke and Duchess of Cambridge's baby boy.
Many tried to glimpse a formal bulletin announcing the 16:24 BST delivery of the baby, who weighed 8lb 6oz.
The King's Troop Royal Horse Artillery and Honourable Artillery Company will fire gun salutes in London later.
Prince William said the couple "could not be happier". Kensington Palace said the baby would be named in due course.
The duke stayed with Catherine and the new arrival - the third in line to the throne - overnight at the private Lindo Wing of St Mary's Hospital, west London.
BBC royal correspondent Peter Hunt said it was unclear how long the baby would be kept in.
The world now awaits the couple's choice of names for their son, who will be known as the Prince of Cambridge.
George is the bookmakers' favourite, followed by James and Alexander.
Meanwhile, at 14:00 BST on Tuesday, the King's Troop Royal Horse Artillery will stage a 41-gun salute in Green Park, after riding past Buckingham Palace.
At the same time, the Honourable Artillery Company - the City of London's army reserve regiment - will fire a 62-gun salute from Gun Wharf at the Tower of London.
'Doing well'
After the new arrival was announced in a statement issued by Kensington Palace, a large cheer went up from well-wishers and journalists outside the hospital.
It is an incredibly special moment for William and Catherine and we are so thrilled for them on the birth of their baby boy"
End QuotePrince Charles
A bulletin - signed by the Queen's gynaecologist Marcus Setchell, who led the medical team that delivered the baby - was taken by a royal aide from St Mary's to Buckingham Palace under police escort.
It was then displayed on an easel in the forecourt of Buckingham Palace in line with tradition.
The notice announced the delivery of the baby, adding: "Her Royal Highness and her child are both doing well."
Kensington Palace said the Duke of Cambridge was present for the birth of his son.
"The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news," a statement said.
The Prince of Wales, in a separate statement, said he and the Duchess of Cornwall were "overjoyed at the arrival of my first grandchild".
"It is an incredibly special moment for William and Catherine and we are so thrilled for them on the birth of their baby boy," he added.
"Grandparenthood is a unique moment in anyone's life, as countless kind people have told me in recent months, so I am enormously proud and happy to be a grandfather for the first time and we are eagerly looking forward to seeing the baby in the near future."
David Cameron: "A wonderful moment"
Royal doctor Mr Setchell described the new arrival as "wonderful baby, beautiful baby", our correspondent added.
Prime Minister David Cameron, speaking outside Downing Street, hailed the "wonderful news".
"It is an important moment in the life of our nation but I suppose, above all, it's a wonderful moment for a warm and loving couple who've got a brand new baby boy," he added.
He said the Royal Family could "know that a proud nation is celebrating with a very proud and happy couple tonight".
Scottish First Minister Alex Salmond said: "I am sure that people across Scotland will be absolutely thrilled to hear the news of the birth of a baby boy to the Royal couple and will want to join me in wishing the proud parents many congratulations."
May God bless this family with love, health and happiness in their shared life ahead"
End QuoteArchbishop of Canterbury
And Welsh First Minister Carwyn Jones congratulated the couple "on behalf of the people of Wales" as "they enter their journey into parenthood".
The Archbishop of Canterbury, meanwhile, said he was "delighted to congratulate the Duke and Duchess of Cambridge on the arrival of their baby boy".
"Along with millions here and around the world, I share in their joy at this special time," added the Most Reverend Justin Welby.
"May God bless this family with love, health and happiness in their shared life ahead."
And US president Barack Obama was among foreign leaders to send their good wishes, saying of the duke and duchess: "We wish them all the happiness and blessings parenthood brings. The child enters the world at a time of promise and opportunity for our two nations."
The Duchess of Cambridge is in labour, as the world's media gather outside the hospital awaiting news of the latest addition to the Royal Family.
Catherine and the Duke of Cambridge arrived by car at St Mary's Hospital in Paddington, west London, at 06:00 BST.
Kensington Palace said she was in the early stages of labour, which was progressing as normal.
The couple do not know the sex of their first child, who will be third in line to the throne.
The world's media have been camped outside St Mary's for days in anticipation of the birth. The due date had never been officially announced but had widely been expected to be mid-July.
Royal vehicles were seen at a back entrance to the hospital at about 06:00 BST, with the announcement coming from Kensington Palace 90 minutes later.
Police presence
The couple, both 31, travelled to the hospital without a police escort, their spokesman said.
The statement from Kensington Palace contains just 45 words.
Such is the global fascination with this baby, those words will be translated into countless languages and endlessly repeated until fresh information is provided once the child has been born.
This intense international interest highlights the challenges facing William and Catherine.
The birth of a child is a deeply personal and private moment. But in their case, it will also be the cause of much wider celebration.
Prince Charles had a similar experience when Prince William was born. He wrote of being rewarded by seeing "a small creature" who "belonged to us even though he seemed to belong to everyone else as well".
Thirty-one years on, the world waits while the Duchess of Cambridge is in labour - something which is not without risk.
Her baby will represent the beginning of family life for the couple and will offer the House of Windsor renewed hope for the future.
The duchess is being tended by a top medical team led by the Queen's gynaecologist Marcus Setchell, who delivered the Countess of Wessex's two children. Alan Farthing, gynaecologist to the Royal Household, will be assisting.
She will give birth in the hospital's private Lindo Wing, where Prince William and his brother Prince Harry were born.
There is a strong police presence around the hospital and two police officers are guarding the entrance to the private wing. The media scrum parked outside is having to contend with the heat on what is the hottest day in the UK since July 2006.
BBC royal correspondent Peter Hunt said the duchess was thought to be one week past her due date.
"The royal statement contains 45 words. All there will be to sustain the world's media until the baby is born," he tweeted.
Last week, the Queen joked about the imminent arrival of the newest member of her family, saying she hoped the baby would be born before she went on holiday to her private Balmoral estate in Scotland.
During a visit to the National Railway Museum in York, the Prince of Wales was asked by the members of the press and the public about the birth of his first grandchild but he did not divulge any information.
Easel announcement
Prince William has been with his wife on annual leave and will have two weeks' paternity leave from his job as an RAF search and rescue helicopter pilot.
It is believed the next time the couple will be seen in public is when they appear on the steps of the hospital with their baby.
Plans for how the birth will be announced were amended by Kensington Palace officials on Monday evening.
A formal press release containing details of the birth will now be issued shortly before a formal signed bulletin leaves the hospital for Buckingham Palace.
It is custom for news of royal births and deaths to be attached to the railings of the palace, but in this case it will be displayed on an ornate easel in the forecourt of the palace.
The Queen, senior members of the Royal Family and the duchess's family - if they are not at the hospital - will be told about the birth first.
Then a royal aide will take a bulletin, signed by key medical staff, from the hospital to the palace under police escort.
The Duke and Duchess of Cambridge's first child will be third in line to the British throne
Under new laws to succession the baby will remain third in line to the throne regardless of gender and the gender of any subsequent siblings.
Prime Minister David Cameron spoke about the excitement surrounding the imminent arrival, and also about the recent changes to the rules of succession.
Speaking on BBC Radio 4's Woman's Hour, he said it was "pretty much a done deal".
'Thoughts and prayers'
All the nations of the Commonwealth have agreed, he said, even if the changes had not yet passed through their parliaments.
The Archbishop of Canterbury, who is likely to carry out any christening, has sent his best wishes to the couple.
There is global interest in the royal birth and it has been the subject of much speculation, particularly when it comes to names.
Bookmaker William Hill says George is the favourite for a boy and, after a flurry of bets, Alexandra - one of the Queen's middle names - for a girl. Charlotte is also thought to be a contender.
The new royal baby will be the Queen's third great-grandchild. It will be expected to take the throne following reigns by Prince Charles and then Prince William.
The couple announced they were expecting their first child in December after the duchess was admitted to hospital suffering from severe morning sickness.
Since the announcement, the duchess has carried out 19 days of public engagements before going on maternity leave in the middle of June.
Catherine's final public appearance before the birth was at the Trooping the Colour ceremony in June.
The Duke and Duchess of Cambridge were married at Westminster Abbey in April 2011, watched on television by hundreds of millions of people around the world.
Seven years ago David Cameron told a Google conference that politicians should encourage companies to change, not over-regulate them.
Today, he announced he had reached agreement with the four biggest ISPs on pornography filters, after some behind the scenes tussling.
But he hinted that if search engines like Google didn't agree to a blacklist of search terms, he would legislate.
From Downing St, he can supplement the art of persuasion with the smack of firm government.
Back in his opposition days, Cameron made waves presenting himself as a man on the side of parents against firms that sold chocolates at checkouts and children's bikinis.
If he can mould a similar image in Downing St, as a PM doing battle with big business on behalf of fellow parents, he will be more than happy.
Mr Cameron also called for some "horrific" internet search terms to be "blacklisted", meaning they would automatically bring up no results on websites such as Google or Bing.
He told the BBC he expected a "row" with service providers who, he said in his speech, were "not doing enough to take responsibility" despite having a "moral duty" to do so.
He also warned he could have to "force action" by changing the law and that, if there were "technical obstacles", firms should use their "greatest brains" to overcome them.
'Innocence'
In his speech, Mr Cameron said family-friendly filters would be automatically selected for all new customers by the end of the year - although they could choose to switch them off.
And millions of existing computer users would be contacted by their internet providers and told they must decide whether to use or not use "family-friendly filters" to restrict adult material.
The filters would apply to all devices linked to the affected home Wi-Fi network and across the public Wi-Fi network "wherever children are likely to be present".
Customers who do not click on either option - accepting or declining - will have filters activated by default, Tory MP Claire Perry, Mr Cameron's adviser on the sexualisation and commercialisation of childhood, told the BBC.
The UK's biggest internet service providers have agreed to the filters scheme meaning it should cover 95% of homes.
Other measures announced by the prime minister included:
New laws so videos streamed online in the UK will be subject to the same restrictions as those sold in shops
Search engines having until October to introduce further measures to block illegal content
Experts from the Child Exploitation and Online Protection Centre being given more powers to examine secretive file-sharing networks
A secure database of banned child pornography images gathered by police across the country will be used to trace illegal content and the paedophiles viewing it
Mr Cameron also called for warning pages to pop up with helpline numbers when people try to search for illegal content.
He said: "I want to talk about the internet, the impact it is having on the innocence of our children, how online pornography is corroding childhood.
"And how, in the darkest corners of the internet, there are things going on that are a direct danger to our children, and that must be stamped out.
Claire Perry MP: "We have asked companies to help families install family friendly filters"
"I'm not making this speech because I want to moralise or scaremonger, but because I feel profoundly as a politician, and as a father, that the time for action has come. This is, quite simply, about how we protect our children and their innocence."
But former Child Exploitation and Online Protection Centre boss Jim Gamble told BBC Radio 4's Today programme it was important to "get to the root cause" of illegal pornography, by catching those responsible for creating it.
He added: "You need a real deterrent, not a pop-up that paedophiles will laugh at."
But Ms Perry argued filters would make a difference, saying that the killers of schoolgirls April Jones and Tia Sharp had accessed legal pornography before moving on to images of child abuse.
She added: "It's impossible to buy this material in a sex shop... but it's possible to have it served up on a computer every day."
In his speech, Mr Cameron said possession of online pornography depicting rape would be made illegal.
Existing legislation only covers publication of pornographic portrayals of rape, as opposed to possession.
"Possession of such material is already an offence in Scotland but because of a loophole in the Criminal Justice and Immigration Act 2008, it is not an offence south of the border," Mr Cameron said.
"Well I can tell you today we are changing that. We are closing the loophole - making it a criminal offence to possess internet pornography that depicts rape."
The move has been welcomed by women's groups and academics who had campaigned to have "rape porn" banned.
Holly Dustin, director of the End Violence Against Women Coalition, said the group was "delighted".
"The coalition government has pledged to prevent abuse of women and girls, so tackling a culture that glorifies abuse is critical for achieving this," she said.
"The next step is working with experts to ensure careful drafting of the law and proper resourcing to ensure the law is enforced fully."
'No safe place'
Mr Cameron, who has faced criticism from Labour over cuts to Child Exploitation and Online Protection Centre's funding, insisted the centre's experts and police would be given the powers needed to keep pace with technological changes on the internet.
Claire Lilley, NSPCC: "In every single child abuse image there is a victim, a child who has been abused"
"Let me be clear to any offender who might think otherwise: there is no such thing as a safe place on the internet to access child abuse material," he said.
A spokesman for Google said: "We have a zero tolerance attitude to child sexual abuse imagery. Whenever we discover it, we respond quickly to remove and report it.
"We recently donated $5m (£3.3m) to help combat this problem and are committed to continuing the dialogue with the government on these issues."
According to some experts, "default on" can create a dangerous sense of complacency, says BBC technology correspondent Rory Cellan-Jones.
He says internet service providers would dispute Mr Cameron's interpretation of the new measures, insisting they did not want to be seen as censors.
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