By James Pomfret and Lidia Kelly
HONG KONG/MOSCOW (Reuters) - An aircraft believed to be carrying Edward Snowden landed in Moscow on Sunday after Hong Kong let the former U.S. security contractor leave the territory, despite Washington's efforts to extradite him to face espionage charges.
The anti-secrecy group WikiLeaks said Snowden was heading for a "democratic nation" which it did not name, although a source at the Russian airline Aeroflot said he would fly on within 24 hours to Cuba and then planned to go to Venezuela.
Moscow airport officials said the flight from Hong Kong had landed but could not immediately confirm Snowden was on board. However, a source at Aeroflot said he had booked a seat on the service.
Snowden, who worked for the National Security Agency, had been hiding in Hong Kong since leaking details about U.S. surveillance activities to news media.
A spokesman for the government of Hong Kong, a former British colony which returned to China in 1997, said it had let Snowden depart because a U.S. request to have him arrested did not comply with the law.
The United States wanted him to be extradited to face trial and is likely to be furious about his departure. In Washington, a Justice Department official said it would seek cooperation with countries Snowden may try to go to.
"It's a shocker," said Simon Young, a law professor with Hong Kong University. "I thought he was going to stay and fight it out. The U.S. government will be irate."
A source at Aeroflot said Snowden would fly from Moscow to Cuba on Monday and then planned to go on to Venezuela. The South China Morning Post earlier said his final destination might be Ecuador or Iceland.
The WikiLeaks anti-secrecy website said it helped Snowden find "political asylum in a democratic country".
It added in an update on Twitter that he was accompanied by diplomats and legal advisers and was travelling via a safe route for the purposes of seeking asylum.
"The WikiLeaks legal team and I are interested in preserving Mr Snowden's rights and protecting him as a person," former Spanish judge Baltasar Garzon, legal director of WikiLeaks and lawyer for the group's founder Julian Assange, said in a statement.
"What is being done to Mr Snowden and to Mr Julian Assange - for making or facilitating disclosures in the public interest - is an assault against the people."
Assange has taken sanctuary in the Ecuadorean embassy in London and said last week he would not leave even if Sweden stopped pursuing sexual assault claims against him because he feared arrest on the orders of the United States.
U.S. authorities have charged Snowden with theft of U.S. government property, unauthorized communication of national defense information and wilful communication of classified communications intelligence to an unauthorized person, with the latter two charges falling under the U.S. Espionage Act.
The United States had asked Hong Kong, a special administrative region (SAR) of China, to send Snowden home.
"The U.S. government earlier on made a request to the HKSAR government for the issue of a provisional warrant of arrest against Mr Snowden," the Hong Kong government said in a statement.
"Since the documents provided by the U.S. government did not fully comply with the legal requirements under Hong Kong law, the HKSAR government has requested the U.S. government to provide additional information ... 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."
It did not say what further information it needed.
The White House had no comment.
CHINA SAYS U.S. "BIGGEST VILLAIN"
Although Hong Kong retains an independent legal system, and its own extradition laws, Beijing has control over its foreign affairs. Some observers see Beijing's hand in Snowden's sudden departure.
Iceland refused on Friday to say whether it would grant asylum to Snowden, a former employee of contractor Booz Allen Hamilton who worked at an NSA facility in Hawaii.
Putin's spokesman, Dmitry Peskov, said earlier this month that Russia would consider granting Snowden asylum if he were to ask for it and pro-Kremlin lawmakers supported the idea, but there has been no indication he has done so.
The South China Morning Post earlier quoted Snowden offering new details about the United States' spy activities, including accusations of U.S. hacking of Chinese mobile telephone companies and targeting China's Tsinghua University.
Documents previously leaked by Snowden revealed that the NSA has access to vast amounts of internet data such as emails, chat rooms and video from large companies, including Facebook and Google, under a government program known as Prism.
China's Xinhua news agency, referring to Snowden's accusations about the hacking of Chinese targets, said they were "clearly troubling signs".
It added: "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."
Venezuela, Cuba and Ecuador are all members of the ALBA bloc, an alliance of leftist governments in Latin America who pride themselves on their "anti-imperialist" credentials.