A Beijing court on Friday sentenced leading dissident Liu Xiaobo to 11 years in prison for subversion, prompting the United States to accuse China of persecuting its political opponents.

The 53-year-old Liu, a writer who was jailed over the 1989 Tiananmen pro-democracy protests, was tried on Wednesday for "inciting subversion of state power" after co-authoring a bold call for political reform last year.

He co-wrote Charter 08, which calls for human rights protection and the reform of China's one-party communist system. It has been signed by more than 10,000 people, according to China Human Rights Defenders, an activist network.

The case has generated concern in the West over China's human rights record, especially in the United States, which urged Beijing to "respect the rights of all Chinese citizens to peacefully express their political views".

"We continue to call on the government of China to release him immediately," US embassy official Gregory May told reporters outside the courthouse following sentencing.

"Persecution of individuals for the peaceful expression of political views is inconsistent with internationally recognised norms of human rights," May said.

Police presence at the courthouse was stepped up Friday, with only the press pack milling around outside the building. A few supporters appeared after the sentence.

A group of Western diplomats including May, who were denied access to Wednesday's proceedings, tried to attend Friday's hearing but were again refused, according to an AFP reporter at the courthouse.

The dissident's wife Liu Xia told AFP that Liu had decided to appeal the verdict.

"He will meet with his lawyers Monday and they will prepare the appeal," said Liu, who had not been allowed to attend Wednesday's trial but was present at her husband's sentencing.

Tight political climate

In a brief dispatch, the official Xinhua news agency reported the sentence in its English-language version only, saying the court had "strictly followed the legal procedures in this case and fully protected Liu's litigation rights".

But rights groups lashed out at what they called a toughening of China's political climate.

"This reverses a trend seen over the past decade towards lighter sentences in subversion cases," Nicholas Bequelin, a senior researcher in the Asia division of Human Rights Watch, told AFP .

The Dui Hua Foundation, a group set up to improve human rights by promoting China-US dialogue, said Liu's sentence was the toughest handed down for subversion since the crime was inscribed in China's penal code in 1997.

In Hong Kong, a group of around 50 people protested against the sentence.

"This decision goes against the international principle of freedom of speech," said Richard Tsoi, vice chairman of the democracy organisation Hong Kong Alliance, which held the march.

On Thursday, Beijing slammed the foreign diplomats who tried to attend Liu's trial and the governments who had made statements on Liu's behalf for what it said was their "gross interference" in China's affairs.

Mo Shaoping, the head of the firm defending Liu, said the writer's case was significant, as he had campaigned for greater human rights and democracy in China for decades.

"He has worked to try to find a way to allow the ordinary citizen to criticise the government or to make proposals to the government, on how the people can participate in government," Mo told AFP on Wednesday.

"We pleaded not guilty -- his crime is a crime of speech."

Wanting less attraction

The subversion charge -- which one of Liu's lawyers, Shang Baojun, said also related to articles posted on the Internet -- is routinely brought against those who voice opposition to China's ruling Communist Party.

Rights activists say China pushes such cases through the courts during the Western holiday season in a bid to attract less global attention.

In 2007, rights activist Hu Jia was arrested on December 27 and charged with subversion. The year before, prominent human rights lawyer Gao Zhisheng was sentenced to three years in prison for subversion just before Christmas.

- AFP