Image copyright AP Image caption Edward Snowden leaked intelligence data to journalists two years ago

Claims that Russia and China have accessed documents stolen by Edward Snowden are a "smear" by "cowards" inside the UK government, a journalist who worked with the whistleblower says.

The Sunday Times reported that Moscow and Beijing had "cracked" a secret cache of files taken by Mr Snowden.

It said some Western intelligence agents had been removed from "hostile countries" because information leaked by Mr Snowden showed how they work.

The Sunday Times stands by its story.

Mr Snowdon's leaks in 2013 revealed surveillance carried out by US intelligence.

Journalist Glenn Greenwald, who helped break the original stories, told the BBC there was "zero evidence" to support claims Russia and China had gained access to the documents.

He criticised what he called "anonymous cowards in the British government" who had spoken to the Sunday Times.

Mr Snowden, now living in Russia, left the US in 2013 after leaking to the media details of extensive internet and phone surveillance by American intelligence.

'Zero evidence'

His information made international headlines in June 2013 when the Guardian newspaper reported the US National Security Agency was collecting the telephone records of tens of millions of Americans.

Mr Snowden is believed to have downloaded 1.7 million secret documents before he left the US.

His actions have been praised by civil liberties campaigners but criticised by intelligence officials, who say the leaks pose security risks.

Mr Greenwald told the BBC's Today programme: "All this story is are people inside the government who have an obvious interest in smearing Snowden.

Image copyright AP Image caption Glenn Greenwald worked on the original Guardian stories in 2013

"They don't have the courage to put their names on these allegations so they remain anonymous.

"There's zero evidence for them. There's all kinds of reasons to believe they're not true.

"It's not journalism it's just acting as subservient stenographers for the government."

According to the Sunday Times, Moscow had gained access to more than one million classified files held by Mr Snowden.

A UK government source told the BBC Russia and China had information that had led to agents being moved but added there was no evidence any had been harmed.

Mr Greenwald said Mr Snowden had told him he did not take documents with him when he went to Russia because he feared he would be hacked.

'Well-informed sources'

He said: "Snowden told me before he left Hong Kong that he had intended to destroy the set and he has said publicly many times that he gave all the copies he had to journalists."

Mr Greenwald said there had been "a huge shift" in the media narrative towards a "pro-Snowden sentiment".

He added: "And as soon as the Snowden narrative shifts, up pops anonymous, unnamed cowards in the British government to smear him with these evidence-free claims and I think that's really the story."

A spokesman for The Sunday Times said: "This story was responsible journalism and another example of The Sunday Times setting the news agenda.

"We reported what various reliable and well-informed sources from within the government told us.

"We fully stand by our story, as did the BBC which also had it confirmed by government sources in its reporting yesterday."