Torture claims

Gao has taken on cases involving the banned Falun Gong spiritual group and defended cases against the government involving alleged police corruption, land seizures and religious freedom.

The petition said the the government has failed to officially arrest and charge Gao with a crime and has not notified his family where he is being held - all violations of Chinese law.

Signatories to the document include Jerome Cohen, a leading expert on Chinese law at New York University; Irwin Cotler, member of Canada's parliament and former minister of justice; and Albert Ho, chairman of Hong Kong's Democratic Party and a member of the territory's legislature.

Western reporters in Beijing have repeatedly pressed China's foreign and public security ministries for information on Gao, but both have declined to provide specifics on his whereabouts.

Following years of legal activism, Gao was convicted of subversion in 2006, but given a suspended sentence.

In 2007, Chinese authorities detained and severely tortured him, threatening to kill him if he disclosed the details of his torture, which he did in 2009, the Washington-based rights group Freedom Now said.

"I hope that the United Nations will ask the Chinese government to follow its own law and to release him," Freedom Now quoted Gao's wife Geng He as saying.

Geng fled China for the United States early last year.

The UN human rights body, whch has no enforcement powers, has not yet commented on the petition.