The Chinese government said on Thursday detained artist and activist Ai Weiwei was being investigated for "suspected economic crimes", while his family said he was the innocent victim of a political witch hunt.
The confirmation from the Foreign Ministry that Mr. Ai faces a police investigation for alleged business-related crimes is unlikely to end the international uproar about his secretive detention, and the departing U.S. ambassador to Beijing, Jon Huntsman, added his voice to the condemnations.
Burly, bearded Ai Weiwei (pronounced "eye way-way") had a hand in designing the Bird's Nest stadium for the 2008 Beijing Olympics, and has juggled a prominent international art career with colourful campaigns against government censorship and political restrictions, often using the Internet.
"It's my understanding that the public security authorities are investigating Ai Weiwei according to law on suspicion of economic crimes," Foreign Ministry spokesman Hong Lei told a regular news conference.
He brushed off Western governments' criticisms.
"China is a country ruled by law and will act according to law. We hope that the countries concerned will respect China's decision," he said. "This has nothing to do with human rights or freedom of expression."
Mr. Hong's brief comments about the investigation echoes an earlier report from the official Xinhua news agency.
Neither he nor Xinhua gave details of the allegations against Mr. Ai, who was stopped on Sunday from boarding a flight from Beijing to Hong Kong and taken away by police, sparking condemnation from Western governments and Chinese human rights campaigners. He has not contacted his family since then.
"The economic crimes report is absurd, because the way he was taken and then disappeared shows it's nothing of the sort," Mr. Ai's older sister, Gao Ge, told Reuters by telephone.
"This is more like a crime gang's behaviour than a country with laws," she said.
Mr. Huntsman, who is soon leaving his post to consider a run as a Republican presidential contender, joined the fray earlier, another sign the case could fester into a diplomatic row between the world's two biggest economies.
"The United States will never stop supporting human rights," Mr. Huntsman said in a speech in Shanghai on Wednesday evening.
Future U.S. ambassadors "will continue to speak up in defence of social activists, like Liu Xiaobo, Chen Guangcheng and now Ai Weiwei, who challenge the Chinese government", said Mr. Huntsman, according to a transcript on the website of the U.S. consulate in Shanghai.
Mr. Liu is the jailed dissident who won the 2010 Nobel Peace Prize, prompting outrage from China. Mr. Chen is a rural legal campaigner under house arrest since being released from jail in 2010.
Mr. Ai's mother, Gao Ying, rejected the charges of "economic crimes", which could cover violations such as tax avoidance, and said they were being used to stifle his activism.
"If he's not released, this will be the start of a long struggle," she told Reuters by telephone. "But they still haven't notified us why he was taken or where he is."
Mr. Ai's campaigning has included voicing support for Nobel winner Mr. Liu and an online campaign to collect the names of children buried in a earthquake in the southwestern province of Sichuan in 2008, many in schools that he and others said were poorly built because of corruption.
Mr. Ai was beaten up by police in Sichuan in 2009, when he was trying to testify for Tan Zuoren, a dissident facing trial, and he told his family then that he may face similar punishment one day, said his sister, Ms. Gao.
"He told us he may have to go to jail one day for his activities, and he was very clear that we shouldn't try to meddle and stop him speaking out," she said. "My mother cried."
Police should have given Mr. Ai's family written notice of where he is and what form of detention he is in, said Liu Xiaoyuan, a Beijing lawyer who said he had given advice to the family.
"The family should have received official notice but hasn't," he told Reuters. "The Xinhua report doesn't have any legal effect. It doesn't mean this is a final charge or anything like that."
On Wednesday, a Chinese newspaper, the Global Times, suggested that Mr. Ai had been testing the bounds of official tolerance. On Thursday, the paper issued new criticism of Western condemnation and reporting about the case and suggested that Mr. Ai was targeted for his political "provocations".
China, it said, "needs people like Ai Weiwei. But at the same time, it is even more important that Chinese law restrict the provocative behaviour of Ai Weiwei and others."
Since February, the government's ingrained fears of challenges to one-party rule have been magnified by online calls for "Jasmine Revolution" protest gatherings inspired by the political flux across the Middle East and North Africa.
Even feeble efforts to act on those calls were smothered by police, but the threat of protests has triggered an unusually broad crackdown. At least three activists have been arrested on subversion charges often used to jail dissidents. In 2009, a Beijing human rights lawyer, Xu Zhiyong, was detained on suspected tax charges before being released after an uproar at home and abroad about vague economic accusations being used to intimidate human rights activists.
Mr. Ai's mother said her son was unlikely to bow to accusations of economic misdeeds to win a swift release.
"He wouldn't surrender just to escape from their hands quickly," she said. "If he's not given justice, he'll refuse to come out, I think. That's his character."