US intelligence leaker Edward Snowden today spent a fourth day at a Moscow airport with his onward travel plans still a mystery after Russian President Vladimir Putin rejected calls for his extradition to the US.

The United States told Russia it has a "clear legal basis" to expel Snowden but anti-secrecy website WikiLeaks, which helped organise his flight from Hong Kong, said he risks being stuck in Russia "permanently".

Meanwhile Venezuela's President Nicolas Maduro, who by coincidence is expected in Moscow next week for an energy summit, said Caracas would consider any asylum request from Snowden just as Ecuador is doing.

In his first comments on the chase for the former contractor that has captivated world attention, Putin yesterday confirmed that Snowden had arrived in Moscow but said he had never left the airport's transit zone.

"He arrived as a transit passenger... He did not cross the state border," Putin said at a news conference in Finland late yesterday. "For us, this was completely unexpected," he added.

"Mr Snowden is a free man, the sooner he selects his final destination point, the better for us and for himself," he said.

Snowden who leaked revelations of massive US surveillance programmes to the media, had been expected to board a flight for Cuba on Monday, reportedly on his way to seek asylum in Ecuador.

But he never did and Putin hinted that his onward travel plans were still unknown. His US passport has been cancelled but WikiLeaks says he left Hong Kong with a refugee document supplied by Ecuador.

Snowden's extended stay in Moscow has prompted comparisons with the Tom Hanks hit film "The Terminal" about a man living in an airport, while British gambling website William Hill has opened betting on his final destination.

"Cancelling Snowden's passport and bullying intermediary countries may keep Snowden permanently in Russia," WikiLeaks said in a statement on Twitter.