BEIJING — A Chinese court sentenced Liu Xiaobo, China’s most prominent dissident, to 11 years in prison for criticizing the government, an unusually long sentence that rights activists say suggests other activists will also face harsh punishment.

The Beijing No. 1 Intermediate People’s Court announced Friday its ruling that Mr. Liu was guilty of “inciting subversion of state power.”

The 53-year-old scholar had spent more than a year in detention before his trial Wednesday, which lasted less than three hours.

Mr. Liu plans to appeal the decision, said one of his lawyers, Ding Xikui. “There were some flaws in the procedures of the trial,” he said, but he declined to comment further. Appeals on sensitive political charges almost never succeed in China, where political directives often supersede the written law.

Mr. Liu has pushed for democratic reforms since the 1980s, and was a participant in the 1989 protests on Tiananmen Square in Beijing. He was detained by authorities last year shortly after he helped write Charter 08, a call for sweeping legal and political change, which hundreds of other scholars also signed.

The letter, which has since attracted thousands of signatures of Chinese citizens, is seen as one of the boldest challenges to Communist Party rule in recent memory.

Mr. Liu’s lawyers said he could have faced a 15-year sentence, but rights groups said the 11-year sentence was still harsh.

The verdict and lengthy sentence, and the fact they were delivered on Christmas, was seen as a rebuke to the outcry from foreign rights activists and governments over Mr. Liu’s case. President Barack Obama, visiting China last month, pressed Beijing to respect “universal” human rights such as free expression, and U.S. officials have repeatedly raised the Liu case with Chinese officials.

Washington criticized the verdict Friday. “We are deeply concerned by the sentence…Persecution of individuals for the peaceful expression of political views is inconsistent with internationally recognized norms of human rights,” U.S. Embassy First Secretary Greg May said at the court Friday morning.

Mr. May repeated his call for China to release Mr. Liu immediately and to “respect the rights of all Chinese citizens to peacefully express their political views.”

The sentence was also another strong message to activists in China, including human-rights lawyers who have received warnings by authorities against taking on political cases.

It also served as a warning to people like Zhao Lianhai, who was formally arrested last week, after a lengthy detention, for organizing families affected by a tainted-milk scandal last year that sickened at least tens of thousands of children.

“The severity of the verdict against [Mr. Liu] suggests that the Chinese government is ready and willing to take an unyieldingly harsh line against human-rights activists in the year ahead,” said Phelim Kine, an Asia researcher with New York-based Human Rights Watch.

“The show trial of Liu Xiaobo by the Chinese authorities is a scandal….We call on President Hu Jintao to reverse this injustice and to release Liu and the scores of other Chinese who have been imprisoned for simply speaking their minds,” said Kwame Anthony Appiah, president of the PEN American Center. Mr. Liu is a member of PEN.

The brevity of the proceedings led many supporters of Mr. Liu to say the trial was just a formality.

Chinese officials couldn’t be reached for comment. The state-run Xinhua news agency reported that a statement from the court said it strictly followed the legal procedures in the case.