A journalist who published the first reports from Edward Snowden's leaked documents offered a detailed rebuttal Monday to allegations that Russian and Chinese spies accessed the former intelligence contractor's files.

Glenn Greenwald, writing on online news website The Intercept, said the reports by the Sunday Times and BBC were based on the false premise that Snowden kept possession of the files he took from the US National Security Agency.

Greenwald, part of a team of journalists who met Snowden in Hong Kong before publishing the explosive articles about vast surveillance programs, said Snowden had kept no files with him when he travelled to Moscow.

"Snowden has said unequivocally that when he left Hong Kong, he took no files with him, having given them to the journalists with whom he worked, and then destroying his copy precisely so that it wouldn't be vulnerable," Greenwald said.

"How, then, could Russia have obtained Snowden's files as the story claims... if he did not even have physical possession of them? The only way this smear works is if they claim Snowden lied, and that he did in fact have files with him after he left Hong Kong."

The Times also reported that Greenwald's partner, David Miranda, had some 58,000 intelligence documents when he was detained at London's Heathrow Airport after visiting Snowden in Moscow.

But Greenwald claimed this was "an utter lie" and that "as of the time he was detained in Heathrow, David had never been to Moscow and had never met Snowden."

The American journalist said the Sunday Times had "quietly deleted" from its online report the claim that Miranda had met with Snowden in Moscow before being detained.

Greenwald also said the Sunday Times "mindlessly" repeated a claim that Snowden downloaded 1.7 million documents when there is no evidence to support the number.

"The NSA has repeatedly said that it has no idea how many documents Snowden downloaded and has no way to find out," Greenwald wrote.

"As the NSA itself admits, the 1.7 million number is not the number the NSA claims Snowden downloaded -- they admit they don't and can't know that number -- but merely the amount of documents he interacted with in his years of working at NSA."

Snowden, who has been granted asylum in Russia, is being sought by Washington which has branded him a hacker and a traitor who endangered lives by revealing the extent of the NSA spying program.

The weekend reports said Britain has been forced to remove some of its spies after Russia and China accessed the raft of top-secret documents.

The Sunday Times said other government sources claimed China had also accessed the documents, which reveal US and British intelligence techniques, leading to fears that their spies could be identified.

An intelligence source told the Sunday Times: "We know Russia and China have access to Snowden's material and will be going through it for years to come, searching for clues to identify potential targets."