In a statement made public on Monday, the UN working group on arbitrary detention said China's government should "provide for reparation of the harm caused" to Gao Zhisheng, who has been missing for nearly a year.
Gao's disappearance has drawn criticism from many human rights organisations and his case is frequently brought up by foreign governments during meetings with Chinese leaders.
Chinese Foreign Ministry spokeswoman Jiang Yu said she was unaware of Gao's whereabouts.
"China attaches importance to cooperation with the UN human rights mechanisms," Jiang said at a regular news briefing in Beijing. "We also urge these mechanisms to maintain an objective and impartial attitude and to respect China's judicial sovereignty.
"I would like to add that China is a country ruled by law, with an independent judiciary that handles cases."
Chinese authorities have intensified a crackdown on lawyers, bloggers and dissidents as the ruling Communist Party clamps down on the risk of unrest, particularly after online calls for "Jasmine" pro-democracy gatherings in the wake of civil unrest in parts of the Middle East.
The whereabouts of Gao, a Christian lawyer who helped defend members of China's banned Falun Gong spiritual group, have been unknown since April last year, when he resurfaced briefly after being abducted from his relative's home in Shaanxi province in early February 2009.
In an opinion piece published on Sunday on the New York Times website, Gao's wife, Geng He, appealed to US President Barack Obama to seek the release of her husband, who has previously claimed he was tortured in detention.