(Reuters) - Twelve Nobel Peace Prize winners have called on British Prime Minister David Cameron to call publicly for the release of their fellow laureate, Liu Xiaobo, and his wife Liu Xia during Chinese President Xi Jinping's visit to London this week.
The laureates, led by South African Archbishop Desmond Tutu, wrote to Cameron on Sept. 2 to urge him to press the couple's case, U.S. advocacy group Freedom Now said.
"We believe that unless leaders like you take urgent action, both publicly and privately, that China will continue to believe it can act with impunity and without consequence for its behavior,” a text of the letter released by Freedom Now said.
The laureates made a similar call to President Barack Obama ahead of Xi's visit to Washington last month. Obama did not bring up the issue in public with Xi.
The Nobel laureates said Liu Xia's health had declined "precipitously" in the past year and she should be allowed to travel abroad for medical care as she had requested.
They said that although the Chinese government said she was under no legal restriction, her apartment was under 24-hour police supervision and her movements were completely restricted.
They said Liu Xia had a heart attack in 2014, suffered from severe back pain, depression and anxiety. They said doctors had warned that her mental health problems would worsen unless there was a change in her living conditions.
Freedom Now founder Jared Genser said that unless Cameron obtained a private commitment for action he should publicly call for their release before the end of the State visit.
Liu Xiaobo, 59, a veteran dissident involved in the 1989 Tiananmen Square pro-democracy protests crushed by the Chinese army, was jailed for 11 years in 2009 on subversion charges for organizing a petition urging an end to one-party rule.
He won the Nobel Prize in 2010.
Xi will be feted by the royal family and leading politicians during his trip to Britain, which Cameron hopes will cement Britain's lucrative place as China's closest friend in the West.
The visit, which will seal a host of business deals, has been criticized by human rights activists who accuse Cameron of turning a blind eye to abuses.
Britain has won praise from China for its discretion in dealing with rights issues by raising them behind the scenes, a policy London says is more effective than public criticism.
Reporting by David Brunnstrom in Washington