The United States said Monday it is "deeply concerned" about the rising trend of disappearances and arrests of human rights activists in China after one of the country's most famous artists was detained.
Ai Weiwei, 53, an avant-garde artist who helped design the futuristic Bird's Nest stadium at the Beijing Olympics, has been missing since he was stopped Sunday while preparing to fly to Hong Kong. Police also raided his Beijing studio.
Dozens of Chinese lawyers and activists have vanished, been detained or held under house arrest since February when online calls for protests similar to the pro-democracy uprisings in the Middle East and North Africa started cropping up. At least three people have been indicted for subversion. No major public protests have taken place in China.
In Washington, State Department spokesman Mark Toner called for the immediate release of Ai, an outspoken government critic who has been keeping an informal tally of the detentions on Twitter, where he has more than 70,000 followers.
"We obviously continue to be deeply concerned by the trend of forced disappearances, extralegal detentions, arrests and convictions of human rights activists for exercising their internationally recognized human right for freedom of expression," Toner told a news conference.
"Our relationship with China is very broad and complex but it's an issue where we disagree and we continue to make clear those concerns," he said.
During a January state visit to Washington, Chinese President Hu Jintao said that his country needed to "do more" on human rights. The White House played up the significance of that admission and said it would be watching to see the Chinese government acted on those words.
Detentions of rights activists have since increased.
Sophie Richardson, Asia advocacy director for Human Rights Watch, said the detention of a well-known figure like Ai was a sign of how far the Chinese government is prepared to go to silence critics. She said the response of the U.S. and other governments to the crackdown has been "sporadic" and urged them to make clear to Beijing such actions would have broad consequences for bilateral relations.
Ai is the son of one of China's most famous modern poets. He was also blocked from leaving China in December on a flight to South Korea. That came shortly after he was invited to attend the Nobel Peace Prize ceremony in Oslo, Norway, honoring jailed Chinese dissident Liu Xiaobo.
Liu is serving an 11-year sentence for subversion.