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.
Waiting for request
But on Saturday, officials in Moscow said they were still waiting for Snowden's request.
Russian Foreign Minister Sergei Lavrov said Snowden would have to submit his application to the Federal Migration Service, Russian news agencies reported.
The head of Russia's Federal Migration Service, Konstantin Romodanovsky, said Saturday it had received nothing. If it did, he added, the request would be examined according to the usual procedures.
Washington has reacted sharply to the possibility that Moscow might offer Snowden a safe harbor.
"We would urge the Russian government to afford human rights organizations the ability to do their work in Russia throughout Russia, not just at the Moscow transit lounge," White House spokesman Jay Carney said.
"Providing a propaganda platform for Mr Snowden runs counter to the Russian government's previous declarations of Russia's neutrality," he added.
US President Barack Obama spoke to Putin by telephone on Friday on issues including the Snowden affair, the Kremlin and White House both said, but no further details were forthcoming.
Washington has already rebuked China for allowing Snowden to leave for Russia from Hong Kong.
At his meeting with activists, Snowden insisted he did not want to harm the US.
It was not clear, however, if this meant he was prepared to stop leaking intelligence in order to stay in Russia.
Venezuela, Bolivia and Nicaragua have all offered Snowden asylum, but Snowden said Western governments would prevent him from traveling to the region.
A summit of the Latin American Mercosur trade bloc issued a statement Friday reaffirming the right to asylum and rejecting "any attempt at pressure, harassment or criminalization by a state or third parties".
The bloc, meeting in the Uruguayan capital Montevideo, denounced four European countries that denied airspace to a plane carrying Bolivian President Evo Morales back from Moscow earlier this month.
