The United States has called on China to immediately release artist and activist Ai Weiwei, saying his detention was inconsistent with the fundamental rights of all Chinese citizens.
State Department spokesman Mark Toner said Washington was "deeply concerned by the trend of forced disappearances, extra-legal detentions, arrests and convictions of rights activists for exercising their internationally recognized human rights."
"The detention of artist and activist Ai Weiwei is inconsistent with the fundamental freedom and human rights of all Chinese citizens," he said. "We urge the Chinese government to release him immediately."
Ai -- best known in the West as a designer of the famed "Bird's Nest" Olympic stadium in Beijing -- was taken into custody on Sunday at Beijing's international airport as he prepared to board a flight abroad, his wife said. His staff said he was going to Hong Kong.
Police in Beijing have refused to explain why they detained outspoken Chinese artist and social critic Ai Weiwei, his wife said Monday, amid fears that authorities are expanding a crackdown on dissent.
"As he was being detained, police came here with a search warrant and searched everywhere," Lu said by telephone.
"They took the computer, computer disks and other materials. They refused to say why the search warrant was issued or why Ai Weiwei was taken away."
Several of Ai's assistants were also detained for questioning on Sunday, but later released, said Lu, adding that she was not under house arrest.
Beijing police refused to comment on Ai's detention when contacted by AFP on Monday.
The artist's detention comes after scores of dissidents, activists, and rights lawyers have been rounded up in recent weeks, with many placed under house arrest or disappearing into police custody.
The clampdown followed anonymous online calls which emerged in February for protests each Sunday around the country to demand political change in China -- aimed at emulating those that have rocked the Arab world.
The disappearance of Ai -- -- whose work is on display at London's Tate Modern gallery until May 2 -- drew immediate concern from numerous human rights groups and Western countries.
Amnesty International said the artist played no part in recent calls for protest, adding that his detention marks a widening of China's crackdown on dissent.
"If the authorities are so bold as to grab this world-renowned artist in broad daylight at Beijing airport, it's frightening to think how they might treat other, lesser known dissidents," said Donna Guest, the group's Deputy Director for the Asia-Pacific.
Urging the international community to speak out against the arrests of bloggers and "cyber-dissidents", Paris-based media watchdog Reporters Without Borders said: "The Chinese government is stepping up its harassment of the remaining prominent dissidents and is trying to silence all of its critics.
France and Germany also condemned the detention and urged China to free Ai immediately.