Edward Snowden is regarded as a hero by some, and a villain by others. Photo: AFP

Reports suggest he will head first to the Cuban capital Havana.

Washington says it expects the Russian government to "look at all options available" to expel him to the US on spying charges - but Russia reportedly says it has "no grounds" to do so.

Mr Snowden initially fled to Hong Kong after leaking secret documents about US internet and phone surveillance.

'Face justice'

Mr Snowden flew from Hong Kong to Russia on Sunday. Officials in Hong Kong say Mr Snowden left the city voluntarily.

But Albert Ho, his lawyer in Hong Kong, told the BBC that a government official urged Mr Snowden to go over the weekend. Mr Ho said he believed the official was acting on the orders of the Beijing government.

He added that his client was given assurances that he would be allowed to leave freely.

The US had been trying to extradite Mr Snowden from Hong Kong, but authorities there said the US request was incomplete and there was no legal basis to stop him from departing.

The US justice department said it was "disappointed" that Hong Kong did not arrest Mr Snowden and that it "disagrees" with its reasons for not doing so.

"We find their decision to be particularly troubling," an official said.

The US state department has urged countries in the "Western Hemisphere" not to let him enter their territory.

"We expect the Russian government to look at all options available to expel Mr Snowden back to the US to face justice for the crimes with which he is charged," Caitlin Hayden, US National Security Council spokeswoman, said on Monday.

She highlighted "intensified co-operation" between the US and Russia after the Boston Marathon bombings in April and their record of working together on law enforcement matters.

But Russia's Interfax news agency quoted an unnamed Russian source as saying: "Snowden has not committed any crimes on Russian territory.

"In addition, Russian law-enforcement agencies have received no instructions through Interpol to detain him. So we have no grounds to detain this transit passenger."

BBC Moscow correspondent Daniel Sandford says Mr Snowden is expected to fly first to Cuba and then to Venezuela before heading to Ecuador. The first plane scheduled to fly to Havana was due to leave Sheremetyevo at 14:05 Moscow time (10:05 GMT).

He will be trying to avoid any country that might arrest him on behalf of the US, our correspondent adds.

'Escorted by diplomats'

Ecuador's Foreign Minister Ricardo Patino said on Monday that Mr Snowden's asylum request was being "analysed".

Ecuador is already giving political asylum to Wikileaks founder Julian Assange, who has been sheltering in its London embassy for the past year.

Wikileaks is now supporting Mr Snowden and said in a statement that he was "bound for the Republic of Ecuador via a safe route for the purposes of asylum, and is being escorted by diplomats and legal advisers from Wikileaks".

Although the US and Ecuador have a joint extradition treaty, it is not applicable to "crimes or offences of a political character".

Mr Snowden left his home in Hawaii after leaking details of his work as an NSA (National Security Agency) contractor and the extensive US surveillance programme to the UK'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 Obama administration is desperate to get its hands on Mr Snowden before he reveals any more secrets, reports BBC Washington correspondent Paul Adams.

A number of prominent politicians have called him a traitor and raised suspicion about the roles played by China and Russia, he adds.

Mr Snowden's 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.

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

US officials have 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.