(CNN) -- Police have taken into custody a Beijing-based scholar known for his criticism of China's policies in the restive western region of Xinjiang, his wife told CNN Friday.
Ilham Tohti, a prominent economics professor belonging to the Uyghur ethnic group, was taken by police on Wednesday afternoon, Guzaili Nuer said, adding that she has not heard from police since and has no idea where her husband is.
In a six-hour operation, around 30 policemen raided their home seizing computers, cellphones, a hard disk, bank cards and Tohti's passport, she said.
Police did not respond to requests for comment.
The U.S. State Department said Tohti, who has been outspoken in support of human rights for China's ethnic Uyghur citizens, had been taken into custody along with at least six of his students.
His detention appeared "to be part of a disturbing pattern of arrests and detentions of public interest lawyers, Internet activists, journalists, religious leaders and others who peacefully challenge official Chinese policies and actions," said Jen Psaki, a State Department spokesperson.
"We call on Chinese authorities to immediately account for the whereabouts of Mr. Tohti and his students and guarantee Mr. Tohti and his students the protections and freedoms to which they are entitled under China's international human rights commitments, including the freedom of expression."
Chinese Ministry of Foreign Affairs spokesman Hong Lei said at a regular briefing on Thursday that Tohti "is suspected of violating the law and committing a crime" and that police have placed him under criminal detention.
Last year saw several outbreaks of violence in Xinjiang, a large, resource-rich region that is home to the Uyghurs, a Turkic-speaking, predominantly Muslim ethnic group.
In December, police shot and killed eight people who attacked police station in western Xinjiang, and a separate clash left 14 Uyghurs and two police officers dead.
Chinese authorities have also blamed Uyghurs for a vehicle attack in Beijing's Tiananmen Square in October that killed five people -- including the three in the vehicle -- and wounded 40 others.
The arrival in Xinjiang of waves of Han Chinese people over the decades has fueled tensions with the Uyghurs. Chinese authorities have cracked down heavily on violence involving Uyghurs, deepening resentment.
CNN's Beijing bureau contributed to this report