More than 300 major authors have signed a petition in support of the imprisoned Chinese dissident Liu Xiaobo.
Wole Soyinka, Salman Rushdie, JM Coetzee and Umberto Eco are among those demanding his immediate release.
Mr Liu was arrested last month after he and hundreds of other Chinese intellectuals issued a wide-ranging call for political reform.
The document, known as Charter 08, challenges the Communist Party's monopoly on power.
Mr Liu is a government critic and veteran of the Tiananmen Square democracy protests in 1989.
He was one of more than 300 prominent Chinese intellectuals to sign the online Charter 08 petition in December.
Released to coincide with the 60th anniversary of the Universal Declaration of Human Rights, the charter called for greater freedoms and democratic reforms in China, including an end to Communist one-party rule.
Mr Liu was arrested by police on 8 December, and is reportedly being held in pre-trial detention "somewhere in the suburbs of Beijing".
Amnesty International has condemned Mr Liu's detention and called on the authorities to make public any information about his alleged crimes.
In December, more than 150 writers and activists from around the world wrote an open letter to China demanding that Mr Liu be freed from jail.
In response, China's foreign ministry said the country was under the rule of law and opposed foreign interference.