Edward Snowden, the former US intelligence contractor turned whistleblower, has been granted a three-year residence permit to remain in Russia.

Snowden's lawyer, Anatoly Kucherena, told reporters on Thursday that Snowden had been granted asylum allowing him to move about freely and travel abroad.

"The request was accepted and accordingly Edward Snowden was given a three-year residence permit," Kucherena said.

The former operative for the National Security Agency (NSA) was granted a one-year temporary asylum last year, but that had run out on August 1.

Snowden, who fled to Hong Kong and then Moscow, is believed to have accessed about 1.5 million secret documents, US officials have said, although how many he actually took is unclear.

Snowden was charged by the US last year over allegations of theft of government property and disseminating classified material to unauthorised people.