BEIJING • A US businesswoman has been held for six months in China over alleged espionage, her supporters said, revealing a case that could complicate Chinese President Xi Jinping's state visit to the United States, beginning yesterday.

China's ministry of state security detained Ms Sandy Phan-Gillis in March and she is being investigated on accusations of "spying and stealing state secrets", according to the website savesandy.org, which provides information on her and her case.

Ms Phan-Gillis was held while crossing the border to Macau at the end of a visit to China by a trade delegation from the Texas oil capital Houston, where she is a member of the mayor's International Trade Development Council, the site said.

The five-member group had visited other Chinese cities, including Beijing, Guangzhou and Shenzhen, and only Ms Phan-Gillis was detained, it added. "Sandy is not a spy or a thief," her husband, Mr Jeff Gillis, said.

Foreign ministry spokesman Hong Lei confirmed the investigation at a regular briefing yesterday. "The person you mentioned... is suspected of carrying out activities endangering national security, and is currently being investigated by relevant departments," he said. "We hope that the outside world will respect China's handling of this case according to law."

It was not clear why the case had not been publicised until Monday, when the announcements were posted to the site.

But the news came as Mr Xi embarked on a visit to the US, beginning with a stop in Seattle before heading to Washington for talks with President Barack Obama.

AGENCE FRANCE-PRESSE