Ai Weiwei has raised enough money to launch an appeal against his 15 million yuan ($2.36 million) tax bill, but authorities are refusing to accept the cash, the artist and dissident's lawyer said Monday.

Ai -- who maintains that the government's tax evasion charge is politically motivated -- had said that he would use more than eight million yuan raised through donations from supporters as a deposit to appeal the bill.

The artist, who spent 81 days in police detention during a crackdown on dissidents this year, had said he planned to submit proof that he had the money needed for the deposit as a guarantee required under Chinese law.

But on Monday -- two days before a deadline to settle the bill -- Ai's lawyer said he had received word from the tax department that they would only accept the deposit if it was paid directly to them.

"They now refuse to accept the guarantee payment, so I need to discuss this matter with Ai Weiwei," Pu Zhiqiang said.

"We have done all we can to try to get a reasonable chance of justice from this country... If we win the lawsuit, I'm worried that there will be trouble with the refund."

Ai was ordered to pay the allegedly evaded back taxes after his release from detention, which sparked a global outcry, and has been given until Wednesday to do so.

On Monday, foreign ministry spokesman Liu Weimin said the case should be "handled in accordance with the law", adding, "it is a fact that Ai Weiwei has evaded a large amount of taxes and there is no doubt over this."

Ai's case is complicated by the fact that the tax charge has been levied against Fake, a company he founded but which is now owned by his wife.

The artist, best known for his role in designing Beijing's "Bird's Nest" Olympic stadium, has denied any wrongdoing and insists the government is trying to silence him and his vocal human rights activism.

Over the past week, some 30,000 supporters have donated money through Internet and bank transfers, while some have even resorted to throwing cash over the walls into his courtyard home, including banknotes folded into paper planes.

Total donations had reached 8.69 million yuan by Sunday night, when the appeal closed.

An official at the Beijing tax office declined to comment when contacted by AFP.