Beijing (CNN) -- China's most famous dissident artist, Ai Weiwei, was being harassed by police and warned to stay away from a planned court appearance on Wednesday, he said.
"I've never seen so many police cars outside my studio -- at one point last night a few dozen were there, which was unprecedented," Ai told CNN by phone.
"Yesterday my assistant wanted to take pictures of the police outside our studio, but his camera was immediately grabbed and he got injured in the process," he said.
"The police started calling me repeatedly yesterday afternoon, warning me to stay away from the court today, which I find pretty confusing" because he is facing tax charges, he said.
Ai says the allegations that he owes back taxes are a cover for accusations that he is trying to overthrow the state.
There were still a handful of police officers around as the artist was due in court, he said.
His wife Lu Qing went to court in his place, the artist said.
Meanwhile, his associate Liu Xiaoyuan was taken by police on Tuesday night, he said.
"I've no idea what's happening to him now, neither do I know why. I don't think we can expect to hear from him any time soon," Ai said.
A Chinese foreign ministry spokesman declined to comment directly on Ai's allegations as he briefed international journalists on Wednesday.
"China is a country of laws," Hong Lei said in response to questions about the dissident. "We rule the country by law. China's constitution and laws protect citizen's legal rights. At the same time, citizens must abide by China's constitution and laws."
Ai said the police actions were "really harming the legal process. They fail to give any explanation for doing so and are contradicting their previous accusations," he said.
The artist, who helped design the iconic Bird's Nest Olympic stadium in Beijing, has endured a difficult relationship with Chinese authorities. Last year he was detained for 81 days and ordered to pay 15 million yuan ($2.38 million) in back taxes which officials said he owed through his company, Fake Cultural Development Ltd.
He paid 8.45 million yuan ($1.3 million) late last year so he could contest the charges. His wife would have been jailed if he had not paid the sum, he said at the time.
CNN's Paul Armstrong in Hong Kong contributed to this report.