A high-profile Chinese dissident accused of subversion was tried at a two-hour hearing Wednesday that shut out foreign diplomats concerned over a case that reflects the communist government's deep suspicion of calls for political reform.

Liu Xiaobo was detained a year ago, just before the release of an unusually direct appeal for more civil rights in China he co-authored called Charter 08, signed by scores of China's top intellectuals. He faces up to 15 years in jail. The verdict is due Friday.

International human rights groups and Western nations have heavily criticized Liu's detention. A dozen diplomats, including from the United States, Britain, Germany, Australia and Canada, stood outside the Beijing courthouse in freezing weather, barred from entering, along with a handful of Liu's Chinese supporters. At least one diplomat said he would try to be present for the verdict.

"We call on the government of China to release him immediately," said Gregory May, first secretary with the U.S. Embassy. The European Union made a similar appeal.

Liu, 53, a literary critic and former professor, spent 20 months in jail for joining the 1989 student-led protests in Tiananmen Square that were crushed in a military crackdown. In his writings, most published only on the Internet, he has strongly called for civil rights and political reform.

Charter 08 demands a new constitution guaranteeing human rights, the open election of public officials, and freedom of religion and expression. Some 10,000 people have signed it in the past year, though a news blackout and Internet censorship have left most Chinese unaware that it exists.

Liu has been the only person arrested over the charter, but rights groups said several signers have been harassed or fired from their jobs, and warned not to attend the trial or write about it online.

However, a few of them risked turning up at the courthouse Wednesday, where dozens of uniformed and plainclothes police were deployed. They passed out yellow ribbons but doubted Liu would go free.

"It's not like we stand out here today and tomorrow China gets democracy," said one signer, 36-year-old Cao Jinbai. "This trial is already decided."

Liu is charged with inciting to subvert state power, a vaguely worded charge that is routinely used to jail dissidents and carries a penalty of up to 15 years in prison.

Liu's wife said she was not allowed to leave her home to attend the trial. Liu's brother-in-law, Liu Hui, was allowed inside and said Liu appeared to be healthy and in good spirits.

Liu admitted "to practicing his freedom of speech, but did not admit to trying to overturn the state's power," the brother-in-law said.