Security services have 'had difficulties tracking terrorists' since the leaks

Home Office official has accused Snowden of having 'blood on his hands'

MI6 has pulled its spies out of 'hostile countries' and America's intelligence agencies are on high alert after Russia and China cracked encrypted files leaked by fugitive whistleblower Edward Snowden.

The top-secret documents contain information that could lead to the identification of British and American spies, according to senior officials in Downing Street, the Home Office and the security services.

A senior Home Office official accused Snowden - the former National Security Agency (NSA) contractor responsible for the biggest confidential information leak in US history - of having 'blood on his hands' after they gained access to over one million files.

Leaked: MI6 has pulled its spies out of 'hostile countries' after Russia and China cracked encrypted files leaked by whistleblower Edward Snowden (pictured) which could identify its agents

Aides in British Prime Minister David Cameron's office have confirmed the top-secret material is now in the hands of spy chiefs in Moscow (President Vladimir Putin, left) and Beijing (President Xi Jinping, right)

Security services have reported increasing difficulties in tracking terrorists and dangerous criminals via email, chat rooms and social media since he exposed Western intelligence-gathering methods, the Sunday Times reports.

Now aides in British Prime Minister David Cameron's office have confirmed the top-secret material is now in the hands of spy chiefs in Moscow and Beijing.

A senior Downing Street source told the Sunday Times: 'It is the case that Russians and Chinese have information.

'It has meant agents have had to be moved and that knowledge of how we operate has stopped us getting vital information.'

A British intelligence source added: 'Snowden has done incalculable damage. In some cases the agencies have been forced to intervene and lift their agents from operations to prevent them from being identified and killed.

nowden said he was protecting 'privacy and basic liberties' by leaking over one million confidential files and claimed America's NSA and British-based GCHQ (pictured) were spying on innocent people

A senior Home Office official accused Snowden, a former contractor at the National Security Agency (NSA), of having 'blood on his hands' after Russia and China gained access to over one million files

Security services have reported increasing difficulties in tracking since Snowden (pictured) exposed Western intelligence-gathering methods

'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.'

Former GCHQ director Sir David Omand believes the leak represents a 'huge strategic setback' which is 'harming to Britain, America and their NATO allies'.

Snowden has done incalculable damage. In some cases the agencies have been forced to intervene and lift their agents from operations to prevent them from being identified and killed British intelligence source

He said the leak could spark a 'global intelligence arms race', adding: 'I have no doubt whatever that programmes are being launched and money is being spent to try and catch up.

'That's probably true not just of China and Russia but a number of other nations who have seen some of this material to be published.

'I am not at all surprised that people are being pulled back and operations where people are exposed are having to be shut down, at least for the moment.'

An official at British Prime Minister David Cameron's office has played down the threat posed to agents by saying there is 'no evidence of anyone being harmed'.

Snowden fled the United States for Moscow in 2013 after he released 1.7 million secret documents from Western intelligence agencies to the media - and has remained under the protection of President Vladimir Putin's regime ever since.

Snowden said he was protecting 'privacy and basic liberties' and claimed America's NSA and British-based GCHQ were carrying out massive surveillance programmes which target millions of innocent people.

Edward Snowden is hailed as a hero by some but a British intelligence source has accused him of doing 'incalculable damage'

David Miranda (left) the boyfriend of the Guardian journalist Glenn Greenwald, was seized at Heathrow in 2013 in possession of 58,000 'highly classified' intelligence documents after visiting Snowden in Moscow

Another intelligence source in the United States said the damage done by Snowden was 'far greater than what has been admitted'.

It is unclear whether Snowden voluntarily handed over the secret documents to remain in Hong Kong and Moscow, or whether the countries stole his data.

But a senior Home Office source said: 'Why do you think Snowden ended up in Russia?

'Putin didn’t give him asylum for nothing. His documents were encrypted but they weren’t completely secure and we have now seen our agents and assets being targeted.'

David Miranda, the boyfriend of the Guardian journalist Glenn Greenwald, was seized at Heathrow in 2013 in possession of 58,000 'highly classified' intelligence documents after visiting Snowden in Moscow.

During the ensuing court hearing Oliver Robbins, then deputy national security adviser in the Cabinet Office, said that the release of the information 'would do serious damage to UK national security, and ultimately put lives at risk'.