More than 40 high-profile Chinese writers, lawyers and activists have sent an open letter to the new leader of the Communist Party, Xi Jinping, urging him to free jailed Nobel laureate Liu Xiaobo.
Signatories, all of whom are based in the mainland, include outspoken legal scholar He Weifang, human rights lawyer Pu Zhiqiang, who has worked with Chinese artist Ai Weiwei, and AIDS activist Hu Jia.
The letter comes as Chinese writer Mo Yan prepares to collect the Nobel literature prize next week.
The verdict against Liu was "wrong", the group said, calling for "the release of Liu Xiaobo and all political prisoners as an initial step of political reform".
Liu was arrested after co-writing Charter 08, a petition that called for the protection of basic human rights and the reform of China's one-party system.
The letter was timed to coincide with "four years since the publication of Charter 08 and the subsequent arrest and sentencing of Liu Xiaobo, and the two years since Liu Xiaobo was awarded the Nobel Peace Prize".
"We believe that the existence of political prisoners does not help China to build its image of a responsible world power," it said.
"Ending political imprisonment is an important benchmark for China to move toward a civilised political system."
The document was addressed to Xi Jinping, who took over as the head of the ruling Communist Party last month and is expected to become president in March, and other top Chinese leaders.
The letter was organised by the Independent China Pen Centre, a grouping of Chinese writers previously led by Liu.
Liu, 56, was awarded the Nobel Peace Prize in 2010, a year after he was sentenced to 11 years in prison for subversion - a punishment that earned international condemnation.
He is one of only three people to have won the award while jailed by their own government.
China strongly condemned his Nobel prize as unwanted foreign interference in its internal affairs, and refused to allow him to attend the ceremony in Oslo - where he was represented instead by an empty chair.
A group of 134 Nobel prize winners from across six disciplines also signed a letter this week calling for Liu's release.
A government spokesman dismissed that call on Wednesday, saying that "China is a country under the rule of law".
Little is known about Liu's current condition - he is said to suffer from hepatitis - because of a curtain of silence drawn across him and his family by Beijing.
Both letters called for the release of his wife Liu Xia, who remains under house arrest at their home in Beijing to prevent her from speaking about her husband's case.