Beijing - Leading international writers, scholars, lawyers and rights advocates on Tuesday urged Chinese President Hu Jintao to free the dissident writer Liu Xiaobo, who is believed to be facing subversion charges for organizing a charter for democratic reform in China.

More than 150 leading US and European-based intellectuals, including award-winning writers Salman Rushdie, Umberto Eco, Seamus Heaney and Hari Kunzru, issued an open letter calling for Liu's release.

"For the international community to take seriously China's oft-stated commitment to respect human rights and the rule of law ... it is urgent that China's central leadership ensure that no one be arrested or harassed simply for the peaceful expression of his or her views," the letter said.

"It is equally urgent that judicial authorities throughout China cease to use China's anti-subversion law to prosecute peaceful critics such as Mr Liu Xiaobo, who should be released immediately without conditions," it said.

The international scholars and writers are the latest to join a growing list of supporters of Liu inside and outside China. Some 1,200 Chinese activists and intellectuals put their names to an earlier petition urging Liu's release.

Liu was arrested two days before the release of "Charter '08," in which the 303 signatories set out their ideals for transforming China into a liberal democracy and lament a lack of "freedom, equality and human rights" under the ruling Communist Party.

"By departing from universal values and a basic political framework, 'modernization' has been a disastrous process that has stripped people of their rights, corrupted normal human feelings and destroyed people's dignity," they said.

Signatory Mo Shaoping, a top lawyer who represents Liu and other dissidents, said he agreed with the charter's principles "because they are universal values and people all recognize them."

"It articulated what all social strata want to say," said Zeng Jinyan, a rights activist who put her name to the charter despite being held under virtual house arrest in Beijing.

Zeng's husband, fellow dissident Hu Jia, was presented in absentia with the European Parliament's Sakharov Prize for Freedom of Thought last week. China sentenced Hu to three and a half years in prison in March for "inciting subversion of state power."

Charter '08 demands sweeping changes to create a "free, democratic and constitutional state," and urges the release of all political prisoners.

It is modelled on the Charter '77 written by intellectuals in the former Czechoslovakia.

It links its blueprint for change to China's 1989 democracy movement, which the party quashed with a brutal military crackdown.

Former Czech Republic president Vaclav Havel, who had signed Charter '77 as a dissident writer, also joined the calls for Liu's freedom on Friday.

"The Chinese government should learn well the lesson of the Charter '77 movement: that intimidation, propaganda campaigns and repression are no substitute for reasoned dialogue," Havel wrote in the Wall Street Journal.

Havel called Charter '08 "impressive," but said, "China in 2008 is not Czechoslovakia in 1977."

"In many ways, China today is freer and more open than my own country of 30 years ago," he wrote in the newspaper. "And yet, the response of the Chinese authorities to Charter 08 in many ways parallels the Czechoslovak government's response to Charter '77."

Apart from arresting Liu, 53, police have reportedly questioned or detained at least 30 other signatories of Charter '08.

Zeng, 25, said police asked her if she had read the charter and she was "aware of the gravity of signing."

"One suggestion: think about this matter; after all, Hu Jia is still in prison," she quoted one of her interrogators as saying.

But some activists said police had not questioned them and the authorities have so far refrained from a mass round-up of the charter signatories.

The government's handling of one of the biggest challenges to its authority since the 1989 democracy movement could determine how it is seen both at home and abroad for the next few years.

"Liu Xiaobo is the most significant Chinese dissident case in a decade," Brad Adams, the Asia director of US-based Human Rights Watch, said in a statement on Tuesday.

"Jailing Liu might serve as a warning to other dissidents, but it would also indicate a political hardening that runs against the current aspirations of the Chinese people," Adams said.

China routinely says all such human rights cases are handled "according to the law" and rejects as "interference" any appeals by foreign groups and politicians.

Asked to comment on Tuesday's open letter urging Liu's release, foreign ministry spokesman Qin Gang told reporters that "China firmly opposes any foreign interference in its internal affairs."

"I can tell you that China runs the country according to law and will handle the relevant issue according to law," Qin said of Liu's case. (dpa)