Image caption Edward Snowden is due to land in Moscow after leaving on a flight from Hong Kong

US intelligence fugitive Edward Snowden has flown out of Hong Kong, from where the US was seeking his extradition on charges of espionage.

His flight is expected to land in Moscow shortly amid speculation he will then fly on to another country.

Hong Kong said Washington had failed to meet the requirements for extradition.

Mr Snowden, an intelligence contractor, fled to Hong Kong in May after revealing details of internet and phone surveillance by US intelligence.

"Mr Edward Snowden left Hong Kong today (June 23) on his own accord for a third country through a lawful and normal channel," the Hong Kong government said in a statement.

Analysis Mr Snowden's departure from Hong Kong was an unexpected turn of events. He had previously said he intended to stay in the city and fight against deportation to the US through the local courts. His leaving removes a major diplomatic headache for the Hong Kong leadership, who were faced with the prospect of a prolonged legal battle. Some observers will say the government took a face-saving way out of a difficult situation. Although the former CIA analyst has gone, he leaves behind many concerns, including revelations that the US government had been spying on several well-known Hong Kong and Chinese institutions. In the same statement announcing Mr Snowden's departure, the Hong Kong government said it had formally written to the US requesting clarification of his reports about the hacking of computer systems here.

On Saturday, the White House contacted Hong Kong to try to arrange his extradition, but the territory's administration now says the documents submitted by Washington did not "fully comply with the legal requirements under Hong Kong law".

As a result, Hong Kong says it requested further information from the US government.

However, the statement goes on: "As the HKSAR Government has yet to have sufficient information to process the request for provisional warrant of arrest, there is no legal basis to restrict Mr Snowden from leaving Hong Kong."

The statement says Washington has been informed of Hong Kong's decision.

Hong Kong has also written to Washington asking for "clarification" following revelations by Mr Snowden concerning the territory - in particular that the US had targeted Hong Kong-based computer networks.

University of Hong Kong law professor Simon Young expressed surprise at the Hong Kong authorities' decision on extradition.

He said that under local law, a very low threshold is required before a provisional warrant can be put in place.

"The US government will wonder why the Hong Kong government feels the surrender paperwork needs to be fully in place before the provisional warrant can be obtained," he said.

Mr Snowden's Aeroflot flight, SU213, is expected to land in Moscow at 17:00 local time (13:00 GMT). But it is not thought he will stay in Russia.

A source at the airline company is quoted by Russian media as saying he will fly on to Cuba and then Venezuela - both countries believed unlikely to comply with a US extradition request.

Whistleblowing website Wikileaks has issued a statement saying that it has helped to find him "political asylum in a democratic country".

Who is Edward Snowden? Age 30, grew up in North Carolina

Joined army reserves in 2004, discharged four months later, says the Guardian

First job at National Security Agency was as security guard

Worked on IT security at the CIA

Left CIA in 2009 for contract work at NSA for various firms including Booz Allen

Called himself Verax, Latin for "speaking the truth", in exchanges with the Washington Post Profile: Edward Snowden

Mr Snowden left the US after leaking details of his work as an NSA (National Security Agency) analyst and the extensive US surveillance programme to Britain's Guardian newspaper and the Washington Post.

He has been charged in the US with theft of government property, unauthorised communication of national defence information and wilful communication of classified communications intelligence.

Each of the charges carries a maximum 10-year prison sentence. The complaint is dated 14 June although it was made public only on Friday.

'Biggest villain'

Confirmation that Mr Snowden has left Hong Kong came only hours after China's official Xinhua news agency condemned the US.

The agency pointed to the latest disclosures by Mr Snowden to the South China Morning Post, along with previous revelations, calling them "clearly troubling signs".

"They demonstrate that the United States, which has long been trying to play innocent as a victim of cyber attacks, has turned out to be the biggest villain in our age," says Xinhua.

Xinhua says Washington should come clean about its record.

"It owes too an explanation to China and other countries it has allegedly spied on. It has to share with the world the range, extent and intent of its clandestine hacking programs."

The blunt commentary by China's Xinhua news agency comes only two weeks after Present Barack Obama met Chinese leader Xi Jinping in California for a summit where cyber security was high on the agenda.

The US warned China that the issue of Chinese "cyber-intrusion" and theft of intellectual property could strain relations, while China said it did not want the issue to become a source of friction.

Beijing university

The latest revelations, published in the South China Morning Post, suggest a Beijing university was targeted.

Further details of Mr Snowden's allegations emerged on Sunday in a report saying that as recently as January this year the NSA hacked into computers and servers at the prestigious Tsinghua University in Beijing.

Image caption The latest revelations suggest US spy agencies targeted Tsinghua University

Mr Snowden is reported as telling the paper that on one single day in January, at least 63 computers and servers at the university were affected.

The South China Morning Post describes the university as home to one of China's "six major backbone networks", from where "internet data from millions of Chinese citizens could be mined".

The leaks have led to revelations that the US is systematically seizing vast amounts of phone and web data under an NSA programme known as Prism.

Mr Snowden said earlier that he had decided to speak out after observing "a continuing litany of lies" from senior officials to Congress.

US officials have since defended the practice of gathering telephone and internet data from private users around the world.

They say Prism cannot be used to intentionally target any Americans or anyone in the US, and that it is supervised by judges.