Prominent rights activist Zeng Jinyan is out of contact and feared to have been detained by police before the opening of the Beijing Olympics, a rights group said.

All attempts to contact Zeng had failed and it’s believed she "disappeared" from her Beijing home on Aug. 7, the Chinese Human Rights Defenders (CHRD) reported.

She has lived under "residential surveillance", or virtual house arrest, for many months and was already prevented by state security police from meeting foreign journalists or speaking to them by telephone.

"The control is tightening," Zeng said in a brief e-mail message on July 10.

Zeng’s husband, prominent dissident Hu Jia, was sentenced to three years and four months in prison in April after a court convicted him of subversion.

The U.S.-based Dui Hua Foundation said Hu’s arrest "cannot escape being connected to the Olympics".

Both Hu and Zeng have spoken out on human rights issues in China and voiced support for the Dalai Lama, the exiled Tibetan Buddhist leader.

"As the Olympics open in Beijing, it is believed that Zeng was taken away to ensure that no journalists will have access to her and that she will be unable to speak out about Hu Jia during the Games," a CHRD statement said.

The statement urged U.S. President George W. Bush, French President Nicolas Sarkozy and International Olympic Committee President Jacques Rogge, to ask Chinese President Hu Jintao to free Zeng.