WASHINGTON: A Chinese researcher who US authorities say hid her ties to the People's Liberation Army has taken refuge in Beijing's San Francisco consulate to avoid visa fraud charges, in a case Beijing said Thursday was "naked political persecution."

According to a court document filed this week in a separate case in California, Tang Juan, a cancer treatment researcher at University of California-Davis, lied about her position as a PLA civilian medical official on her visa application last year.

The document filed Monday, in the separate visa fraud case of PLA-tied researcher Song Chen, said that after FBI agents interviewed Tang on June 20, she took refuge in the Chinese consulate in San Francisco.

The Tang and Song cases are the latest in a series of US arrests of Chinese researchers for allegedly hiding their ties to the PLA or Chinese Communist Party in visa applications to study or do research in the United States.

Tang's status was mentioned in Song's case to justify a federal prosecutor's argument that the recently arrested Song should not be released on bail because she is likely to try to flee the country. The cases come amid boiling trade, military and diplomatic tensions between Washington and Beijing.

On Wednesday, the State Department said it had ordered China to shut its consulate in Houston, accusing Beijing of ramping up spying and intellectual property theft operations.

"These activities have increased markedly in scale and scope over the past few years," the department said. Asked early Thursday about Tang, Chinese Foreign Ministry spokesman Wang Wenbin said he had no information to release at the moment.

However, Wang said, the US government "has continually monitored, harassed and even arbitrarily detained Chinese students and scholars in the US, and accused Chinese scholars on the presumption of guilt." "This is naked political persecution," he said. "China will take necessary measures to safeguard Chinese citizens' safety and legitimate rights."