Beijing systematically dismantled CIA spying efforts in China beginning in 2010, killing or jailing more than a dozen covert sources, in a deep setback to US intelligence there, The New York Times reported on Sunday.

The Times, quoting 10 current and former American officials who spoke on condition of anonymity, described the intelligence breach as one of the worst in decades.

It said that even now intelligence officials are unsure whether the US was betrayed by a mole within the CIA or whether the Chinese hacked a covert system used by the CIA to communicate with foreign sources.

Of the damage inflicted on what had been one of the most productive US spy networks, however, there was no doubt: at least a dozen CIA sources were killed between late 2010 and the end of 2012, including one who was shot in front of colleagues in a clear warning to anyone else who might be spying, the Times reported.

In all, 18 to 20 CIA sources in China were either killed or imprisoned, according to two former senior American officials quoted. It was a grave setback to a network that, up to then, had been working at its highest level in years.

Those losses were comparable to the number of US assets lost in the Soviet Union and Russia because of the betrayals of two infamous spies, Aldrich Ames and Robert Hanssen, the report said.

Source: Khaleej Times