One of China's most celebrated human rights lawyers was detained Tuesday, an associate told AFP, a month before the highly sensitive 25th anniversary of the 1989 Tiananmen Square crackdown.

Pu Zhiqiang was held by police in Beijing "over charges of creating disturbances", said lawyer Si Weijiang.

"He is now held at the Beijing No. 1 detention centre," Si said.

Authorities routinely round up outspoken critics of the Communist Party in the weeks before key events.

Pu -- who has represented dissident artist Ai Weiwei and is a prominent rights campaigner -- attended a seminar in Beijing on Saturday to mark the brutal suppression of huge anti-government protests in Tiananmen Square, according to online reports.

Academics and other members of China's rights movement attended the event, along with the mother of a dead protester, the reports said.

Democracy activist Hu Shigen, who was among the attendees, was also detained soon after the event, said the overseas campaign group China Human Rights Defenders.

"Hu Shigen also criminally detained at Beijing No. 1 detention centre," it said on Twitter.

Hu was released from prison in 2008 after serving 16 years of a 20-year sentence for trying to organise memorials for the Tiananmen massacre.

Hundreds of people -- by some estimates, thousands -- died in the June 4, 1989 crackdown. Beijing called the demonstrations a "counter-revolutionary riot".

Some of Pu's associates said online that he was initially questioned by police soon after the meeting.

An official from Beijing police told AFP he was unable to comment when asked about Pu's detention.