Artist Ai Weiwei, the most high-profile victim of a sweeping crackdown on activists in China, returned home late Wednesday after nearly three months in detention, saying he was fine and conditions of his release meant he could not say more.

The official Xinhua News Agency said Ai had confessed to tax evasion, accusations his family had long denied and which activists had denounced as a false premise for detaining him. He has spoken out strongly against the ruling Communist Party, and his family and supporters called his detainment punishment for speaking out about the communist leadership and social problems.

Ai, looking tired and thinner than he did before he was taken away on April 3, walked through the gate of his suburban home studio shortly after 11 p.m. with his mother and wife. He said his health was fine as he thanked reporters for their support outside his studio. But he said he remained under restrictions and could say no more.

"I'm sorry I can't (talk), I am on probation, please understand," Ai said, speaking in English.

The conditions appeared to extend also to Ai's family, although his mother told reporters she was relieved to see him again. "I'm so happy that my son is back," Gao Ying said.

Ai's detention and disappearance had sparked an international outcry, with the United States and other countries saying it was a sign of China's deteriorating human rights situation.

German Foreign Minister Guido Westerwelle was cautiously optimistic about Ai's release.

"That would be a big relief for the artist and his family, even though the reported circumstances of his release on bail continue to appear depressing," Westerwelle said in a written statement.

Several of Ai's work colleagues have also been detained, but there was no immediate word on their fate.

Hundreds of Chinese lawyers, activists, and other intellectuals have disappeared or been questioned or detained by authorities in the ongoing clampdown, and those released have almost universally kept silent, possibly fearing repercussions.

The three-paragraph Xinhua report said Ai was released because of his poor health and because he had shown a "good attitude in confessing his crimes" and pledging to pay taxes he owed.

Xinhua repeated allegations in state media that a company linked to Ai, Beijing Fake Cultural Development Ltd., had evaded a "huge amount" of taxes and intentionally destroyed accounting documents.

Formal charges against Ai have never been announced, and the state media report did not mention any pending charges or trial. It is extremely rare for detained people to be released on bail in China.

Ai's wife Lu Qing said the company in question is registered and belongs to her, not him. The company handles the business aspects of Ai's art career.

'Highly dubious grounds'

Sophie Richardson, Asia advocacy director for Human Rights Watch, said Ai will likely face onerous restrictions on his activities and contact with the outside world for some time, based on the experience of others recently released.

The "highly dubious grounds" on which Ai was detained and the apparent lack of due process in his release called into question China's often-repeated claim to be a country ruled by law, Richardson said.

"The rule of law is whatever they say it is, whenever they say it is," she said by phone from Washington D.C.

Well-known British sculptor Anish Kapoor, who dedicated one of his latest monumental works to the imprisoned artist, said he was delighted with the news but wanted Ai to have a fair chance to answer the accusations against him.

While I am thankful that he has been released, I do not think that artists should present their work in China until the situation has been resolved," Kapoor said in a statement.

Ai is among China's most internationally known artists and had a hand in designing Beijing's iconic Bird's Nest Olympic stadium before souring on the event. His fame has soared in recent years, both for his groundbreaking art and his bold irreverence toward authority.

Informal tally on Twitter

Ai's detention at Beijing's airport on April 3 made him the most famous victim of a sweeping crackdown against dissent in China that began in February when online calls for protests similar to those in the Middle East and North Africa began to circulate.

Ai had been keeping an informal tally of the detentions on Twitter.

Ai was held under a form of detention known as residential surveillance somewhere outside Beijing. His wife was permitted one brief, monitored meeting in which she said he seemed well cared for and was not being held in a formal jail.

Ai, 54, suffers from high blood pressure and diabetes. He told Lu during her May visit that he was taking long walks everyday, had his blood pressure checked seven times a day, and was eating and sleeping well.

Ai has also spoken critically about a number of national scandals, including the deaths of students in shoddily built schools that collapsed during the 2008 Sichuan earthquake, children killed or sickened by tainted infant formula and a deadly high-rise fire in Shanghai that killed 58 and was blamed on negligent workers and corrupt inspectors.