BEIJING » Chinese avant-garde artist Ai Weiwei said Saturday authorities would keep him under house arrest for at least another 24 hours to prevent him from attending a party commemorating the forced demolition of his newly built studio in Shanghai.

Ai, who has become known as much for his social activism as his art in recent years, was planning to fly to the Chinese financial hub for Sunday’s celebration, but people he suspects were police told him Friday that he would not be permitted to leave his Beijing home.

"I’m under house arrest to prevent me from going to Shanghai. You can never really argue with this government," Ai, 53, said.

"They’ve told me I would be held until midnight Sunday and I would be prevented from leaving before then," he said.

Ai said the men refused to identify themselves and it wasn’t clear who gave the order to detain him. On Saturday afternoon, three plainclothes officers watched outside Ai’s home in an artists’ colony on the eastern edge of the city, but did not prevent an Associated Press Television reporter from entering to interview him.

Ai, who is also an architectural designer, said he had been invited by the head of Shanghai’s suburban Jiading district to build a studio on a plot of farmland containing a derelict warehouse. He said he was initially reluctant, but eventually agreed and spent two years designing and building the studio, only to receive notice in July that the building was an illegal structure and would be knocked down.

Other artists invited to build on the site were unaffected by the order and Ai said he was later told that he had been singled out for political reasons.

He speculated the order was payback from Shanghai officials for his frequent blogging about the revenge killing of six city police officers by a man who had allegedly been tortured and the case of Feng Zhenghu, a Shanghai activist who camped out at Tokyo’s international airport for nearly 90 days after Chinese officials barred him from returning home.

"They’re very contradictory," Ai said, referring to Jiading district officials. "They asked that I donate the building to the government for a museum, but how could I do it if it’s an illegal structure?"

"This is an organized crime style of doing things," he said.

The son of one of China’s most famous modern poets, Ai was courted by the communist government as a cultural ambassador before his advocacy on behalf of social activists apparently made him a target of internal security.

Known for distinctive scraggly beard and stocky frame, Ai was a consultant for the futuristic Bird’s Nest stadium at the Beijing Olympics before souring on the event. He was later beaten and detained while attempting to attend the trial of an advocate for victims of the devastating 2008 earthquake in the southwestern city of Chengdu.

Ai has exhibited and contributed to projects throughout Europe and the United States, and an installation of his involving 100 million porcelain sunflower seeds is currently on display at the Tate Modern gallery’s famed Turbine Hall in London.

In typical fashion, Ai had planned to commemorate the demolition of his studio with a party catered with river crabs — a Chinese homophone for the government’s catch phrase of "harmonious." Critics sarcastically use the term to describe policies such as censorship and the demolition of working class homes to make way for flashy new developments.

Ai said about 2,000 people had signed up to attend, including fellow artists, musicians, and members of the media.

The gathering has been canceled, although Ai said many would-be attendees still planned to visit the space on Sunday.

Ai’s detention comes amid a crackdown on China’s small, embattled dissident community prompted by the awarding last month of the Nobel Peace Prize to imprisoned Chinese dissident writer Liu Xiaobo.

Liu’s wife and a number of friends and colleagues have been held at police stations or placed under detention in their homes to prevent them from expressing their support. That treatment that is expected to continue at least until the award ceremony in Oslo, Norway, on Friday.

Beijing was enraged by the awarding of the prize to Liu, and has responded by issuing a hail of diatribes denigrating Liu, the Nobel Peace Prize committee, and the West in general and pressuring foreign countries not to send representatives to attend the award ceremony.