Duncan Hewitt: "Xu Wenli has been a thorn in the side of the Chinese authorities for many years"

Xu Wenli, of the China Democracy Party (CDP), was taken from his Beijing home on Monday night, according to his wife, He Xintong.

She said more than 20 police officers then spent almost four hours searching their home before removing a computer, fax machine and address books, as well as documents, many connected with the CDP.

The move has been condemned by the United States.

James Rubin: "A serious step in the wrong direction"

The State Department spokesman, James Rubin, described it as "a serious step in the wrong direction."

He said the matter had been raised with the Chinese authorities, and added: "We have said for some weeks now that we are disturbed by the recent number of detentions of dissidents that serve to limit political debate in China."

Others also detained

BBC Beijing Correspondent Duncan Hewitt: Arrests signal official crackdown on pro-democracy movement

Mr Xu - a veteran pro-democracy campaigner released in 1993 after spending 12 years in jail - was recently nominated head of the CDP's Beijing branch.

His wife said she believed his detention could be connected with this.

The dissident has been questioned by police on a number of occasions in recent months, but his wife said this was the first time police had shown a formal detention warrant - which allows a suspect to be held for up to a month.

At the same time, activists who recently founded a CDP branch in the central city of Wuhan were also detained.

These included Qin Yongmin, a close ally of Mr Xu, and two others, according to a Hong Kong-based dissident group, the Information Centre of Human Rights and Democratic Movement in China.

Activists fear more arrests

Catherine Baber of Amnesty International, Hong Kong: The latest in a worrying number of prosecutions

The centre suggested that the detentions were in response to a meeting in Wuhan last week of local members of the CDP.

Another party member was also reported to have been detained in the eastern city of Hangzhou, where attempts to establish China's first independent political organisation began this summer.

Xu Wenli has already spent 12 years in jail

The Hong Kong centre said it believed the latest moves could herald a tougher line from authorities concerned at growing support for the group. In the past, activists have been questioned, but the majority later released.

Activists are thought to have been emboldened by China's recent signing of the UN's covenant on civil and political rights, which guarantees the right to establish political parties.

National People's Congress Chairman Li Peng was reported on Tuesday as saying that any political organisation pushing for a multi-party system "will not be allowed to exist".