China has warned the international community it had "no right to interfere" in the case of outspoken artist Ai Weiwei, who has been detained for investigation of unspecified economic crimes.
Hong Lei, a foreign ministry spokesman, confirmed a state media report on Thursday that Ai was the subject of a police probe, and claimed that Ai's arrest was not a human rights issue.
Ai, who helped design the Bird's Nest Olympic Stadium for the 2008 Beijing Games, was detained in Beijing on Sunday while trying to board a flight to Hong Kong and has not been heard from since.
Western governments and rights groups have lined up in support of Ai but Beijing signalled it would not tolerate criticism from abroad.
"Ai Weiwei is under investigation on suspicion of economic crimes," Hong told reporters during a briefing, refusing to comment on the nature of the alleged crimes.
"It has nothing to do with human rights or freedom of expression," he said, in the first official Chinese comment on Ai's case.
"Other countries have no right to interfere," added Hong, who later refused to answer further queries on Ai and abruptly cut the briefing short when the questions continued.
Ai, who was born in 1957, is the latest of dozens of activists and government critics rounded up following online calls for demonstrations in China to emulate the "Jasmine" protests that have rocked the Arab world.
The United States, France, Germany and Britain have joined Amnesty International and other groups in calling for Ai's release, with Jon Huntsman, the US ambassador, defending the artist in a Shanghai speech on Wednesday.
In unusually blunt public comments, Huntsman - who will soon leave his post - saluted Ai, jailed Nobel peace laureate Liu Xiaobo and others who "challenge the Chinese government to serve the public in all cases and at all times".
China typically uses charges such as subversion to put away government critics, as it did in Liu's case, but has also previously levelled accusations of various economic crimes such as tax-related offences to silence others.
Police on Sunday also raided the Beijing studio run by Ai - a burly man with a distinctive wispy beard whose work is currently on display in London's Tate Modern gallery.
The son of a poet revered by China's early Communist leaders, Ai has become a thorn in the government's side.
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.