Image copyright AFP Image caption A man (R in blue tie) identified as Jerry Chun Shing Lee by Hong Kong media

An ex-CIA agent has pleaded guilty to spying for China, the US justice department says, in a case believed to be linked to the dismantling of a US espionage network.

Jerry Chun Shing Lee, 54, left the CIA in 2007 to live in Hong Kong, where he was recruited by Chinese agents.

Prosecutors say the naturalised US citizen was then paid to divulge information on US covert assets.

This led China to bring down a network of informants between 2010 and 2012.

About 20 informants were killed or jailed during that period - one of the most disastrous failures of US intelligence in recent years.

The US Assistant Attorney General for National Security, John Demers, said Lee's case was the third involving US agents and China in less than a year.

"Every one of these cases is a tragic betrayal of country and colleagues," he said.

What did Lee do?

Lee, who worked for the CIA between 1994 and 2007, pleaded guilty to conspiracy to deliver national defence information to aid a foreign government in a court in Virginia on Wednesday, the justice department said in a statement.

It said Lee was contacted by the Chinese intelligence agents in 2010. They offered him money, promising to take care of him "for life" in exchange for the required secret information. Hundreds of thousands of dollars were deposited in his Hong Kong bank account between May 2010 and December 2013.

Mr Lee created a document containing information about CIA activities, including locations to which US agents would be assigned.

In 2012, FBI agents searched a hotel room in Hawaii registered in Mr Lee's name and found a USB drive. Investigators found the document on unallocated space in the drive, suggesting it had been deleted.

The search also revealed Lee to have a day planner and address book containing notes of intelligence provided by CIA agents, their true identities, operational meeting locations and phone numbers, and information about covert facilities.

Lee was interviewed by CIA officers in 2012 during which he said he had met Chinese intelligence officers but concealed the fact that they had set him tasks, the justice department said. In 2013 he first denied knowing about the document on his USB drive and then admitted he had created it but said he had never handed it on to Chinese agents.

Mr Lee was arrested at New York's JFK airport in January 2018. He will be sentenced in August.

Spy v Spy

By Tara McKelvey, BBC News, Washington DC

The Lee case shows that the battle between Chinese and US spies has intensified over the past year, turning into a new "Cold War", as Michael Collins, the deputy assistant director of the CIA's East Asia mission center, called it.

The Chinese are investing more resources into their efforts to ferret out information about the US government, while the US government has become more aggressive in its pursuit of US citizens who have helped Chinese agents.

And when the guilty party is a former CIA officer, one of their own, the men and women who work in the field of US intelligence are ready to "bring the hammer down", one senior intelligence official said.

CIA spy operation in China: Key dates

Image copyright AFP Image caption Chinese police guard the US embassy in the capital, Beijing