The United States on Wednesday repeated its demand that Russia return American intelligence leaker Edward Snowden to face justice.

US Secretary of State John Kerry called his Russian opposite number Sergei Lavrov after reports that Russian authorities had given Snowden permission to leave a Moscow airport transit area and formally enter the country after four weeks in limbo.

"He reiterated our belief that Mr Snowden needs to be returned to the United States where he will face a fair trial," State Department spokeswoman Jen Psaki said.

Kerry also told Lavrov that Snowden's "been accused of three felony counts, he is not a human rights activist. He is somebody who's been accused of leaking classified information and that Russia still has the ability to do the right thing and facilitate his return."

Although Washington was still "seeking an update on the exact status" of Snowden whereabouts "any move that would allow him to depart the airport would be deeply disappointing," she told reporters, adding that Washington believed the former CIA-contractor was still in the transit lounge of a Moscow airport where he has been since June 23.

Earlier, White House press secretary Jay Carney told reporters aboard Air Force One: "We're seeking clarity from Russian authorities about Mr Snowden's status and any change in it."

"He has been charged with serious felonies for the unauthorized leaking of highly classified information," he said. "Mr Snowden should be expelled and returned to the United States."

There were conflicting reports Wednesday from Moscow about whether Snowden would be allowed to leave the transit area of Moscow's Sheremetyevo Airport.

Snowden has been marooned at the airport amid an international tug of war set off by his revelations about highly secret US electronic surveillance programs.

Russian news reports said he had been given a document allowing the former IT contractor to leave the transit area and cross the Russian border, but a lawyer who has been helping him denied that.

Psaki also highlighted that the United States had in the past cooperated with Russian requests for their nationals to be returned to Moscow, saying "we don't have a formal extradition treaty, as you know, with Russia, but we have returned several hundred, I believe, individuals to Russia."

Asked for further information on who had been returned to Russia and over what time frame, she said she could not get into specifics but would check for further details.