CHENGDU, China – A Chinese dissident who posted essays on the Internet that criticized communist authorities has disappeared and may have been abducted by the security services, an advocacy group said Friday.

Huang Qi, founder of the human rights Web site 64Tianwang, was forced to get into a car by three unknown men on Tuesday evening in the southwestern city of Chengdu, Reporters Without Borders said Friday.

The Paris-based group said two other activists, whom it didn't further identify, were abducted with Huang.

The group, known by its French initials, RSF, said it believed Huang may have been taken away by police or agents of the State Security Ministry because of articles he has posted criticizing the government's response to the May 12 earthquake that devastated a wide swathe of Sichuan province, of which Chengdu is the capital.

“The abduction of Huang and his two companions one month to the day after the Sichuan earthquake shows that the crackdown on press freedom activists continues,” Reporters Without Borders said.

RSF said Huang's disappearance came one day after Zheng Hongling, a retired university professor, was detained after posting a three articles about the earthquake and the government's response on a Web site hosted in the United States.

China's security forces have begun to clamp down on dissent after initially tolerating independent reporting on the quake and allowing public complaints by parents who blame corruption and shoddy construction on school collapses that killed their children. In recent days, parents and volunteers have been rounded up and threatened and foreign media forced to leave quake-damaged areas.

Calls to an office number used by Huang in the past rang unanswered and two lawyers who represented him in his earlier trial said they had no longer kept in contact with him and were unaware of his whereabouts.

An officer at the Chengdu police spokesman's office said it had a policy of not answering questions over the phone and referred inquiries to the local Communist Party committee's propaganda department, where phones rang unanswered.

Huang has long been one of China's most outspoken activists. Earlier this decade, he served a five-year prison sentence on subversion charges linked to politically sensitive articles posted on his Web site, which could not be accessed Friday.

Since his release in 2005, Huang, who is in his mid-forties, has supported a wide range of causes from aiding families of those killed in the 1989 military crackdown on pro-democracy protests in Beijing, to publicizing the complaints of farmers involved in land disputes with authorities.

Most recently, the former computer engineer had written a series of Internet postings criticizing aspects of the massive relief effort, alleging skewed reporting by the entirely state-controlled media, and accusing the government of obstructing the work of non-governmental organizations, RSF said.

“Few citizens trust the government because of the corruption scandals that already occurred during similar disasters in the past,” it quoted him as saying in one posting.