Human rights group Amnesty International has expressed shock at the reports that a prominent Chinese human rights lawyer and activist was returned to prison.

China's official news agency said Friday that Gao Zhisheng has been sent back to prison for three years after a Beijing court ruled he had violated the terms of his probation.

Catherine Baber, Asia-Pacific deputy director at Amnesty International issued a statement calling the news shocking. She said nothing has been heard from Gao in 20 months and that his family has not known if he is dead or alive.

A brief report from the Xinhua news agency was the first word of Gao's whereabouts or status since he emerged briefly from secret detention in April of last year.

Baber said there is nothing lawful about the way the authorities have handled Gao Zhisheng's case.

Gao was sentenced to three years in prison in 2006 for inciting subversion of state power. He was given five years of probation, effectively sparing him from prison, but has been detained without charges almost continuously since 2009.

Gao's wife, Geng He, left for the United States in early 2009 with their two children.

The lawyer, an outspoken critic of the government, has worked for the rights of some of China's most vulnerable people, including persecuted Christians and miners working in unsafe conditions.

Human rights advocates often cite Gao's case along with that of Liu Xiaobo, the jailed academic awarded the 2010 Nobel Peace Prize, as examples of what they say is the Chinese Communist Party's increasing persecution of human rights defenders in China.