By Humeyra Pamuk

WASHINGTON (Reuters) – The United States on Tuesday said it was deeply concerned about China’s detention of Xu Zhangrun, a law professor who has been an outspoken critic of the ruling Communist Party, and urged Beijing to release him.

Xu, 57, a professor at the prestigious Tsinghua University, came to prominence in July 2018 for denouncing the removal of the two-term limit for China’s leader, which allows Xi to remain in office beyond his current second term.

According to a text message circulated among Xu’s friends and seen by Reuters, he was taken from his house in suburban Beijing on Monday morning by more than 20 policemen, who also searched his house and confiscated his computer.

“We are deeply concerned by the PRC’s detention of Professor Xu Zhangrun for criticizing Chinese leaders amid tightening ideological controls on university campuses in China. The PRC must release Xu and uphold its international commitments to respect freedom of expression,” U.S. State Department spokeswoman Morgan Ortagus wrote in a tweet.

The detention comes as a new national security law came into effect in Hong Kong last week. The sweeping legislation that Beijing imposed on the former British colony punishes what China defines as secession, subversion, terrorism and collusion with foreign forces, with up to life in prison.

Critics say the aim of the law is to stamp out a pro-democracy movement that brought months of protests, at times violent, to the city last year.

The imposition of the new law further deteriorated ties between Washington and Beijing, which had been at loggerheads for months over the handling of the coronavirus pandemic and a nearly two-year trade war.

On Monday, U.S. Secretary of State Mike Pompeo said the United States is “certainly looking at” banning Chinese social media apps, including TikTok, suggesting it shared information with the Chinese government, a charge it denied.

(Reporting by Humeyra Pamuk; Editing by Sandra Maler and Alistair Bell)