Demonstrators demanding the release of Nobel Peace laureate Liu Xiaobo and to redress miscarriage of justice of the June 4, 1989 pro-democracy movement, confront police during a protest in Hong Kong.

Beijing - Activists urged China to release dissident Liu Xiaobo from prison and his wife from house arrest on Friday, one year after Liu won the 2010 Nobel Peace Prize.

US-based Human Rights Watch called for all nations that attended last year's prize ceremony to “use the anniversary to call for Liu's freedom and for an end to the illegal persecution of his family and supporters.”

“The Chinese government is put on notice when presidents and prime ministers publicly express concern about the treatment of people like Liu,” said Sophie Richardson, the group's China director.

“All those who demonstrated support for him should press for his release and for an end to the persecution of others like him,” she said.

The Hong Kong-based China Human Rights Defenders urged all Nobel Peace Prize laureates - including US President Barack Obama, the Dalai Lama, Nelson Mandela and Friday's 2011 winner - to campaign for Liu's release.

It appealed to China's ruling Communist Party to free Liu; end the house arrest of his wife, Liu Xia; and “cease the intimidation of Liu Xiaobo's family and supporters.”

Liu Xiaobo, 55, a prominent writer and one of China's leading dissidents, was sentenced to 11 years in prison in December 2009 for his part in writing Charter '08 for democratic reform.

China reacted angrily when the Nobel committee chose him for the peace prize. It boycotted the awards ceremony in Oslo in December when the jailed writer was represented by an empty chair.

Police placed Liu Xia under house arrest at the couple's Beijing apartment after the announcement of the Nobel prize on October 8.

Two days after the announcement, state security police took Liu Xia to visit her husband at a prison in the north-eastern city of Jinzhou, but the police have since isolated her and cut off her mobile phones.

“I have never seen the blue wall outside the main gate to my home. Is it the sea?” Liu Xia asked in one of her last, sarcastic Twitter messages in mid-October.

The police erected high blue screens to hide the front of the compound from throngs of foreign reporters while assertive plain-clothed security officers guarded the gates.

Earlier this week, the blue screens and most of the police had vanished, but a security guard said foreign visitors were still banned from the compound.

It was not clear if Liu Xia, 51, was still held there. She has been reportedly prevented from contacting anyone except for weekly meetings with her parents.

Many Beijing-based rights activists continued to support the couple.

Dissident Hu Jia, who was released from prison in June, said he tried to visit their apartment in August but was barred by security personnel.

Liu Xiaobo's brother, Liu Xiaoxuan, said Chinese authorities allowed Liu Xia to visit her husband in July for the first time in more than eight months.

“From the first time, we were told that we can only discuss family affairs,” Liu Xia said of her earlier prison visits.

“If we talk about anything else, the meeting can be cut off immediately,” she told dpa in an interview shorty before the announcement of last year's peace prize.

Guards allowed them to share their love of poetry and literature during the visits and had let Liu Xiaobo read and write, Liu Xia said.

“But mainly, I just tell him I live well outside and which friends I've met and had dinner and drinks with,” she said. “He would be glad to hear this.”

Liu Xiaoxuan published a poem dedicated to his brother on overseas websites last month, lamenting his “high-walled isolation.”

He told the Hong Kong-based Information Centre for Human Rights and Democracy this week that his brother was allowed to leave prison briefly to attend their father's funeral on September 18.

Authorities also allowed Liu Xiaoxuan and Liu's two other brothers to visit him in prison last month, he said.

But Human Rights Watch said the release of information on the visits and Liu Xiaobo's attendance at the funeral appeared to reflect the Chinese government's “calculated and cynical strategy to blunt international criticism.”

Renee Xia, the international director of China Human Rights Defenders, agreed that the move was “likely a calculated effort to soften the image of the government” ahead of Friday's announcement of the 2011 Nobel Peace Prize.

“But we would accept nothing short of freeing Liu Xiaobo as a real step toward progress,” Xia said. - Sapa-dpa