The Chinese government "systematically dismantled" CIA spying efforts in China from late 2010, killing or imprisoning at least a dozen covert CIA sources in the following two years, The New York Times reported on May 21.
The New York 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.
Some investigators believed there was a mole within the CIA, while others suspected that the Chinese had hacked the covert system the CIA used to communicate with its foreign sources. The debate remains unresolved, the newspaper said.
At least a dozen CIA sources were killed from late 2010 until the end of 2012, including one who was shot in front of colleagues in the courtyard of a government building as a warning to others, The New York Times reported.
In all, 18 to 20 CIA sources in China were either killed or imprisoned, according to two former senior American officials who were quoted.
Those losses were comparable to the number of U.S. assets lost in the Soviet Union and Russia because of the betrayals of two infamous spies, Aldrich Ames and Robert Hanssen, the report said.
Western intelligence services have traditionally found it exceptionally hard to develop spy networks in China and Russia.
By 2013, the FBI and CIA concluded that China no longer had the ability to identify American agents, the paper reported.
Both the CIA and the FBI declined to comment.
The revelations come as the CIA seeks to determine how some of its highly sensitive documents were released two months ago by WikiLeaks, and the FBI examines possible links between the campaign of U.S. President Donald Trump and Russia.
The Trump administration has appointed Terry Branstad, who is the governor of Iowa, as its ambassador to China, but he has not yet moved to Beijing.
With additional reporting by Reuters, AP, and BBC