Officials briefing reporters declined to discuss the circumstances of the arrest of Juan Tang, a researcher at the University of California at Davis who was charged with lying about her military service in China on her U.S. visa application.

© Bloomberg U.S. Pursues Chinese Researcher At San Francisco ConsulateA Chinese flag flies outside the China Consulate General building in San Francisco on July 23.

Days after U.S. agents interviewed Tang last month, prosecutors filed a criminal complaint against her in federal court, under seal.

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On Thursday, a spokesman for the Chinese Foreign Ministry accused the U.S. of “political persecution” in the case, but stopped short of saying whether Tang was being sheltered by diplomats. “We urge the U.S. to stop using any excuse to limit, harass and crack down on Chinese scholars and Chinese students in the U.S.,” spokesman Wang Wenbin told a regular news briefing in Beijing.

The criminal complaint, unsealed July 20 in a Sacramento, California, federal court, accused her of falsely denying connections to the Chinese military and the Chinese Communist Party. Tang applied for a U.S. visa in October to study cancer treatments at University of California Davis, located just outside of Sacramento.

An FBI agent said in the complaint that Tang had apparent connections to the military, based on an Internet search of news articles. Agents interviewed her at her apartment in Davis last month and seized electronic material under a search warrant. Tang denied any connection to the military or the Communist Party, but agents found a photograph of her in military uniform in the electronic material. Tang told the agents she was required to wear the uniform to attend medical school because it was run by the military.

They also found an application for government benefits in which she listed her political affiliation as a communist party member, according to the agent’s affidavit.