Human rights groups and Western officials welcomed Ai´s unexpected release on bail, but voiced dismay over the conditions and urged Beijing to free other activists still in police custody.[break]
Ai was freed late Wednesday because of his "good attitude" in confessing to tax evasion, his willingness to repay taxes he owes, and on medical grounds, the government said.
His detention -- which came during a major government crackdown on activists launched in February -- sparked furious criticism led by Western governments who repeatedly called for his immediate release.
The release of the 54-year-old avant-garde artist comes just before Chinese Premier Wen Jiabao sets off Friday on a European tour, with stops in Hungary, Britain and Germany.
London and Berlin have been especially vocal about the case. Ai´s work has been displayed this year at the British capital´s Tate Modern gallery, and the University of the Arts in Berlin has invited him to be a guest professor.
"I´m fine. I´m very happy to be free and I´m very happy to be back with my family," Ai told AFP by telephone early Thursday.
Later in the day, after an outing with his family, the artist -- wearing a white t-shirt bearing his name -- emerged from his home in an artists´ district on the northern outskirts of Beijing, looking tired and a little thinner.
"I can´t talk about the case. I can´t say anything," he told about 20 reporters, mostly from the foreign media.
The artist, whose work is often showcased abroad, said he would stay at home for a few days and confirmed to reporters: "I can´t leave Beijing." He then asked the press to leave.
Ai´s cousin, Zhang Jinsong, was also released Thursday afternoon, Ai´s sister Gao Ge told AFP.
Human Rights Watch welcomed the artist´s release as a "relief for his family, friends and supporters", but pointed out that "troubling unanswered questions about his arrest, detention and conditions of release" remain.
The New York-based group said it was "concerned about the political nature of his arrest, the conditions under which the police may have extracted a ´confession´ from him, and possible restrictions on freedoms he faces".
Chinese foreign ministry spokesman Hong Lei told reporters that Ai was "still under investigation" for economic crimes and not allowed to leave Beijing "without permission". His bail agreement is valid for 12 months.
When asked about international pressure over Ai´s case, Hong replied: "China is a country under the rule of law. We hope the relevant countries respect China´s judicial sovereignty."
He added that the development in Ai´s case would have "no influence" on Wen´s trip to Europe as it involved a "very common economic crime".
Rights groups are now clamouring for the release of other activists who have disappeared into police custody since mid-February when Beijing, nervous about online calls for Arab-style protests, clamped down on dissent.
"It is vital that the international outcry over Ai Weiwei be extended to those activists still languishing in secret detention or charged with inciting subversion," Amnesty International´s Asia-Pacific Deputy Director Catherine Baber said.
Ai should be granted "full liberty, and not be held in illegal house arrest as has been the pattern with so many others recently released from arbitrary detention," Baber added.
There was no visible police presence at Ai´s home, but a surveillance camera was positioned outside the front gate.
Paris-based media watchdog Reporters without Borders noted that Ai´s release did not necessarily mean "the end of his problems", saying he could still be convicted and face "an exorbitant fine".
The son of a poet revered by China´s early Communist leaders, Ai helped design the Bird´s Nest Olympic Stadium for the 2008 Beijing Games, but has since angered authorities with his activism and criticism of the government.
He probed the collapse of schools in the 2008 Sichuan earthquake, looked into a Shanghai high-rise fire last November that killed dozens, and says police beat him when he tried to testify on behalf of another activist in 2009.
German Chancellor Angela Merkel said Ai´s release "can only be a first step", calling for the allegations against him to be clearly explained.
"Now, the accusations that have been made against (him) must be explained in a transparent manner and in conformity with the rule of law," she said in a statement released by her office Wednesday.
European parliament president Jerzy Buzek insisted that Ai´s arrest "was both unjustifiable and unacceptable".
Ai joined Merkel, Facebook founder Mark Zuckerberg, and Myanmar´s democracy icon Aung San Suu Kyi this year in Time magazine´s annual list of the world´s 100 most influential people.
Two men who identified themselves to AFP as Chinese artists who knew Ai approached his house and pasted two white posters reading "I love you Ai Weiwei" on the front gate, one in English and the other in Chinese.
They left quickly, declining further comment.