BEIJING: A civil rights activist who recently spoke out about China's ''black jails'' - unofficial detention centres used to discourage people from complaining to the Government - claims he is now being held against his will in one of those jails.

Zheng Dajing said he was detained on Friday with other people who were marking China's annual Legal Publicity Day - meant to promote awareness of China's legal system - with protests in Beijing.

China has denied the existence of black jails, but a state-run magazine last month described the secret detention centres where petitioners - citizens who come to Beijing with complaints about corruption in their home towns - are held and sometimes beaten.

The report said officials were under pressure to reduce the number of petitioners and that they paid people to detain those who come to Beijing before they could complain.

Human Rights Watch, in a report last month, estimated there were up to 50 black jails in Beijing alone.

The China-based organisation Chinese Human Rights Defenders reported that Mr Zheng, from central Hubei province, was an organiser of the protests, but Mr Zheng said he was merely standing near a Beijing railway station observing a protest when he was taken away.

''We were just standing there watching,'' Mr Zheng said. ''They must have detained thousands of people'' around the city, he said.

However, the rights group said there were no other reports of mass detentions.

Mr Zheng, 48, stood behind a locked metal door, whose screen window was covered with semi-opaque plastic, and answered questions on Saturday. The location was a two-storey building in the dim courtyard of a hotel in a west Beijing alley.

''I have no idea when I can leave,'' he said.

Mr Zheng was being watched by a guard inside the locked room who protested loudly at first to the interview but then walked away. Other guards earlier on Saturday had stopped his wife from seeing him, he said.

Mr Zheng said he and others were taken to Majialou, which Chinese Human Rights Defenders described as ''a central black jail for petitioners'', for processing before being taken to his current location, a dingy guesthouse with ''Siyuan Hotel'' spelled out in neon lights. He said he and three other people were being held there.

He said guards hit his wife, Cao Xiangzhen, and pulled her hair when she tried to enter to speak to him. She said the same earlier on Saturday. Mr Zheng, who has spoken to foreign media before about being held in black jails, said he had not been beaten.

Last month's surprisingly open report in the state-run magazine Outlook said officials pay black jail operators 100 yuan ($16) to 200 yuan a day for each petitioner held captive.

A man who came out of the Siyuan Hotel and ended the interview with Mr Zheng said: ''This is police business. Take it up with the police.''

He would not give his name but said he worked with the hotel.

''No comment,'' he said when asked about black jails. ''Get out.''

Associated Press