Prominent Chinese dissident Gao Zhisheng, a lawyer who first disappeared into police custody nearly two years ago, has been imprisoned in the far western region of Xinjiang, his brother said on Sunday.

The United States, the European Union and the United Nations have called on Beijing to release Gao, who has defended some of China's most vulnerable people including Christians and coal miners.

He was arrested in February 2009 and has been held largely incommunicado by authorities except for a brief release in March 2010.

"I received the decision letter this morning saying Gao Zhisheng is in Shaya prison in Xinjiang," his brother, Gao Zhiyi, told AFP. He added the document was issued by a Beijing court.

After Gao briefly reappeared more than 20 months ago following his apparent release by police, friends and colleagues he spoke with reported that he continued to be tailed by authorities and was in ill-health.

In April 2010 he disappeared again and has not been heard from since. The charges against him were never made public but he was arrested in 2006 for "subversion".

The prison, located in Xinjiang's Aksu prefecture, could not be reached by telephone on Sunday. Xinjiang is traditionally regarded as China's gulag for receiving political prisoners in the 1950s and 1960s.

The official Xinhua news agency said last month that Gao had been sent back to prison for three years after a court ruled he had "seriously violated probation rules a number of times".

Bob Fu, head of the Texas-based rights group China Aid, likened the jailing in Xinjiang to internal exile.

"The Chinese government can use this remote jail to prevent concerned people to visit attorney Gao," Fu said in a statement.

Speaking from his home in northern Shaanxi province, Gao Zhiyi said he will attempt to visit his brother later this month.

"I did not know where my brother was for over a year. I always knew that he was not free and he was under control of the government and state security," he said.

Last month, the United States urged China to "immediately release" Gao and to clarify his whereabouts.

"We are especially concerned about Gao's welfare and whereabouts, including reports that his family has been unable to communicate with him," a State Department spokeswoman told reporters.