The United States called Tuesday on China to free an outspoken professor who was detained after criticizing President Xi Jinping over the coronavirus pandemic.

Xu Zhangrun, a law professor at Tsinghua University, one of China's top institutions, was taken from his home in suburban Beijing on Monday along with more than 20 other people, his friends said.

"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," State Department spokesman Morgan Ortagus said, referring to the People's Republic of China.

"The PRC must release Xu and uphold its international commitments to respect freedom of expression," she wrote on Twitter.

A woman in the original coronavirus epicenter of Wuhan walks in May 2020 past a picture of Chinese President Xi Jinping, who faced rare open domestic criticism over his virus response from a professor who has since been detained
A woman in the original coronavirus epicenter of Wuhan walks in May 2020 past a picture of Chinese President Xi Jinping, who faced rare open domestic criticism over his virus response from a professor who has since been detained AFP / Hector RETAMAL

Xu was one of the rare prominent figures to offer open critiques of Xi, who has clamped down hard on dissent.

In an essay in February that appeared on websites overseas, Xu blamed a culture of deception and censorship fostered by Xi for the spread of COVID-19.

The United States in recent months has stepped up its denunciations of China on multiple fronts including human rights.

President Donald Trump has blamed a poor Chinese response for the global spread of COVID-19, which was first detected in Wuhan, although both Beijing and US critics accuse Trump of deflecting criticism over his own handling of the crisis.

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