Edward Snowden possesses data that could prove far more "damaging" to the US government that he has chosen not to release, said a journalist who first broke the story.

Glenn Greenwald told Argentina's La Nacion newspaper that Snowden, the fugitive whistle-blower who is currently stranded in Moscow, had only sought to alert people that information they thought was private was being exploited by US intelligence agencies.

"Snowden has enough information to cause more damage to the US government in a minute alone than anyone else has ever had in the history of the United States," he told the paper in an interview published on Saturday.

"But that's not his goal," said Greenwald, who published a series of stories in Britain's Guardian newspaper based on top-secret documents about sweeping US surveillance programs that were leaked by Snowden.

His comments came as Russia waited on Sunday for a promised request for asylum from Snowden.

The US wants the former US National Security Agency contractor returned to face trial over the leaks. Moscow has so far rejected that demand.

Snowden, 30, has been stranded in the transit zone of Moscow's Sheremetyevo International Airport, after the US withdrew his passport on his arrival from Hong Kong three weeks ago.

Snowden on Friday dramatically summoned Russian activists to his temporary base, to say he wanted to claim asylum in Russia until he could safely travel to Latin America for a permanent sanctuary.

He withdrew an initial request earlier this month after Russian President Vladimir Putin said he would have to stop releasing information embarrassing to Washington if he wanted to stay.

Human Rights Watch accused Washington of trying to block Snowden's attempts to claim asylum and said that was in violation of his rights under international law.

Representatives from both organizations attended Snowden's presentation.