TAIPEI (AFP) - More than 140 Nobel laureates led by archbishop Desmond Tutu urged China on Wednesday to release Nobel Peace Prize winner Liu Xiaobo, a rights activist jailed for subversion since 2009.

In a letter also signed by 400,000 people from more than 130 countries, the laureates called on China's president-in-waiting Xi Jinping to release Mr Liu and his wife Liu Xia, who has not been charged but is being held under house arrest.

The petition was being submitted to Chinese embassies and diplomatic missions in Hong Kong, New York, Paris, Berlin and London.

"This flagrant violation of the basic right to due process and free expression must be publicly and forcefully confronted by the international community," archbishop Tutu, a fellow Peace laureate, said in the petition.

In Taiwan, Mr Wu'er Kaixi, a former leader of the 1989 Tiananmen protests and one of those who signed the petition, urged Beijing-friendly President Ma Ying-jeou to relay the appeal to Mr Xi.

"Hopefully through the petition, President Ma would do something that would help the Chinese government's release of Liu Xiaobo and his wife," he told AFP.

Another Tiananmen protest leader Wang Dan, who like Wu'er Kaixi lives in exile in Taiwan, also signed the document.

In a previous statement commemorating the Tiananmen protests, Mr Ma called on the Chinese government to release Mr Liu as a step towards political reform while pressing for exchanges with the island.

"The first step in political reform is to tolerate dissidents and cherish their value and contribution to society," Mr Ma said.

Mr Liu, who was awarded the Nobel Peace Prize 2010, was sentenced to 11 years in prison in 2009 on subversion charges after co-authoring Charter 08, a bold petition calling for political reform in his Communist-ruled homeland.