China 'crippled CIA by killing or imprisoning informants'

The Chinese government "systematically dismantled" CIA spying operations in China and killed or imprisoned up to 20 informants over a two-year period, according to reports.

Quoting 10 current and former US officials who spoke on condition of anonymity, the New York Times described the intelligence breach as "one of the worst in decades".

Between 18 and 20 CIA sources were killed or imprisoned in China between 2010 and 2012, the Times claimed.

One informant was shot in front of colleagues in a clear warning to anyone else who might be spying, the paper claimed.

The losses were comparable to the number of CIA assets lost in the Soviet Union and Russia as a result of betrayals by two infamous spies - Aldrich Ames and FBI agent Robert Hanssen, who were arrested in 1994 and 2001, respectively - the report said.

Some investigators suspected a former CIA operative of being a mole, but failed to gather enough evidence to arrest him and he is now living in another Asian country, the report said.

But others have rejected the mole theory believing instead that the Chinese had hacked the covert system the CIA used to communicate with its foreign sources.

The Chinese activities began to emerge in 2010, when the US spy agency had been getting high quality information about the Chinese government from sources deep inside the bureaucracy, four former officials told the Times.

The information began to dry up by the end of the year and the sources began disappearing in early 2011, the report said.

As more sources were killed the FBI and the CIA began a joint investigation of the breach, examining all operations run in Beijing and every employee of the US Embassy there.

By 2013, the FBI and CIA concluded that China no longer had the ability to identify American agents, the report said.

The revelations come as the CIA is trying to determine how some of its highly sensitive documents were released two months ago by WikiLeaks, and the FBI examines possible links between Donald Trump's election campaign and Russia.

Both the CIA and the FBI have declined to comment on the report.