A Xian-based dissident has disappeared after organising a petition for the release of fellow activist Yang Jianli, a human rights watchdog reported yesterday.
Zhao Changqing, 34, has been missing since last Wednesday, New York-based Human Rights in China said.
The group quoted a friend of Mr Zhao, dissident Zhang Zhongai, as saying police in Xian, Shaanxi province, had identified Mr Zhao as the mastermind behind a campaign for Yang's release.
Yang, who was born in China but holds United States permanent residency, was arrested in Kunming, Yunnan province, in April after entering the country to investigate widespread labour unrest.
Mr Zhao had collected 170 signatures for the release of 38-year-old Yang, the rights group said.
Mr Zhao was jailed for six months after the 1989 Tiananmen crackdown. He was released from jail in March last year after serving three years on charges of endangering state security.