Ai Weiwei fans have again rallied behind the outspoken Chinese artist after he revealed he is being investigated on pornography charges -- by posting naked pictures of themselves online.

Supporters of Ai -- who disappeared into custody for 81 days earlier this year -- this month donated nearly nine million yuan ($1.4 million) to the artist after he was handed a huge bill for alleged back taxes.

Now, his fans are taking a different tack to counter a police investigation into photos of the 54-year-old in which he and a group of women pose nude, sitting on traditional wooden chairs in the middle of a bare white room.

Dozens of supporters have posted naked or part-naked photos of themselves on a blog page titled "Ai Wei Fans' Nudity -- Listen, Chinese government: Nudity is not Pornography".

Some of them are full-frontal and revealing. Others are more discreet, with the Chinese character for "love" -- pronounced the same as "Ai" -- or pictures of the artist placed across their private parts.

One man poses as sculptor Auguste Rodin's famous "Thinker" statue, another emulates Michelangelo's "David".

The blog can be viewed at http://awfannude.blogspot.com/view/flipcard.

Ai, an artist of international renown whose vocal rights activism has irked the Chinese government, was taken into secret police detention in April and released in June.

He denies the charge of tax evasion, calling it politically motivated, and on Friday told AFP that authorities had accused him before of producing pornography.

"When they detained me, they said 'this is pornography', but I just laughed, I said, 'do you know what is pornography?'" he said. "Nudity is not pornography."

He said he had not taken the charge seriously until his assistant was pulled in for questioning last week about his pictures.

"This is completely ridiculous. Our nation today is so corrupt, with so much sex, but they think nudity photos on the Internet is pornography," he said.

Ai's problems with the authorities started when he began investigating the collapse of schools in the 2008 Sichuan earthquake and a 2010 fire at a Shanghai high-rise that killed dozens.

But until his detention he had been left relatively unscathed thanks to his family background. His father is the late Ai Qing, a famous poet who was disgraced and later rehabilitated by the Communist regime.

The artist caused another stir at the weekend when he published the mobile numbers of four prominent figures online in protest at blog posts and articles they had written about him, accusing them of trying to damage his reputation.

The four were subsequently deluged with texts and calls. One of these, Hu Xijin, is the editor of the state-run, nationalistic Global Times newspaper, which published an editorial Tuesday slamming the artist for the move.

"This is a prominent case in which political dissent drives people to take immoral activities," it said.

Ai has accused Hu and three others of trying to harm his image through blog posts and articles they wrote during his detention and after he was freed, adding they have the state's support.