Chinese police called more people in for questioning Tuesday as they expanded their investigation into avant-garde artist Ai Weiwei, who has not been heard from since being taken into custody over the weekend, friends said.
Ai, an outspoken government critic, was last seen early Sunday in police custody after he was barred from boarding a flight at a Beijing airport. His disappearance comes as the security services carry out a massive crackdown on lawyers, writers and activists following online calls for protests in China similar to those in the Middle East and North Africa. No public protests have emerged.
The European Union delegation in Beijing on Tuesday joined the U.S. and Britain in expressing concern over Ai's case, deploring the ramped-up detention of government critics.
Dozens have recently been taken into custody with little word from authorities about where they are being held, who is holding them or what crimes they are suspected of committing.
"We call on the Chinese authorities to refrain from using arbitrary detention under any circumstances," the delegation said in a statement.
Police appear to be working their way down a detailed list of both Chinese citizens and foreigners associated with Ai, calling them in for questioning, said Alison Klayman, an American filmmaker who has been working on a documentary about the artist.
Police searched Ai's home and studio shortly after his detention and removed computers and other items.
Ai's wife, Lu Qing, said friends and family were asking police for information about his whereabouts and that of an assistant, Wen Tao, who was detained along with him. So far, they had learned nothing, Lu said.
"I am very worried," Lu told The Associated Press by telephone. "I felt something terrible was going to happen when they came to search the house and took away all those things."
Lu said that friends of Ai and people who have collaborated with him are being contacted for questioning.
A Beijing police spokesman, speaking on routine condition of anonymity, said he had no information on Ai's case. Under Chinese law, police are supposed to notify family members when detaining a suspect for longer than 24 hours, though authorities often make exceptions in politically charged cases, as Ai's appears to be.
There has been no word from Ai since he was escorted away by two officials while clearing customs at Beijing Capital International Airport on his way to board a flight for Hong Kong.
It was not clear why the 53-year-old artist and architectural designer was barred from leaving or who was now holding him.
Ai, a star in international art circles, has been barred from going abroad at least once before. He has grown increasingly critical of China's communist authorities and had been keeping an informal tally of those recently detained on Twitter, where he has more than 70,000 followers.
U.S. State Department spokesman Mark Toner called Monday for Ai's immediate release, saying Washington was "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."
British Foreign Secretary William Hague said Monday he was very concerned about Ai's disappearance and said London was committed to engaging China on human rights issues.
Ai is the son of one of China's most famous modern poets, and that stature led many to believe he was protected from serious attack or formal arrest. He had been courted by the government as a cultural ambassador before his advocacy on behalf of social activists apparently made him a target of Chinese authorities.
Among China's best known artists internationally, Ai recently exhibited at the Tate Modern gallery in London.
He was stopped from boarding a flight to Seoul in December, shortly after being 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.
Ai said at the time that police blocked him at the boarding gate and showed him a handwritten note that said he could cause damage to national security by leaving.
Known for his distinctive scraggly beard and stocky frame, Ai was a consultant for the futuristic Bird's Nest stadium at the Beijing Olympics before souring on the event. He was later beaten and detained while attempting to attend the trial of an advocate for victims of the devastating 2008 earthquake in the southwestern city of Chengdu.
Speaking by phone from New York, Klayman said Beijing police visited Ai's studio three times in the past week, checking the passports and identification of Chinese and foreign assistants working there along with some visiting architecture students from Europe.
Associated Press writer Isolda Morillo contributed to this report.