A Chinese security ministry official has been arrested on suspicion of spying for the US and passing on state secrets, Hong Kong media reports say.
The man, who was private secretary to a vice-minister in the security ministry, was arrested earlier this year, various press reports say.
US Secretary of State Hillary Clinton declined to comment on the reports.
If confirmed, it would be the third major incident to hit China-US relations in the past few months.
It would also be the highest-level spy case involving China and the US to become public since 1985, when intelligence official Yu Qiangsheng defected to the US.
The official had been recruited by the CIA, local press and Reuters report.
'Pretty woman trap'
Hong Kong-based Oriental Daily quotes the monthly New Way as saying on 25 May that the official "fell into a pretty woman trap" set up by the CIA.
After the two were photographed in secret liaisons, he was blackmailed and agreed to supply secret information to the US, the reports say.
"The destruction has been massive," a source told Reuters.
The official was arrested between January and March on allegations that he had passed information to the US for several years on China's overseas espionage activities, Hong Kong press and Reuters report.
China's foreign ministry did not respond immediately to a request for comment faxed by Reuters on Friday.
China-US relations have been fraught with tension in recent months, following two high-profile cases.
In March, rising political star Bo Xilai was sacked as Communist party chief in the city of Chongqing, after his police chief fled to the US consulate in the city of Chengdu in neighbouring Sichuan province.
And earlier this month, blind activist Chen Guangcheng left for a new life in New York, after he caused a diplomatic crisis by escaping from house arrest and seeking refuge in the US embassy in Beijing.
It would put further pressure on China's security chief, Zhou Yongkang. Rumours were swirling about his possible downfall in the wake of Mr Bo's sacking, wrote the BBC's Beijing correspondent Damian Grammaticas at the time.
Most China-US spy cases involve industrial espionage. Last year, an Indian-born engineer was found guilty in the US state of Hawaii of selling military secrets to China to do with the B-2 bomber.
In 2003, a US woman who had been recruited to spy on China by the FBI was arrested along with her lover, a former FBI agent, but a judge later dismissed the charges against her.