Beijing, China (CNN) -- A Chinese court upheld an 11-year prison term for a prominent dissident sentenced for subversion late last year, a court official said Thursday.
The Beijing High People's Court provided no additional details on the case.
Liu Xiaobo, 53, was detained on December 8, 2008, and held under "residential surveillance" as police investigated his case, according to the PEN American Center, a U.S. literary and human rights organization.
In June, he was arrested and charged with inciting subversion of state power, the organization said. Liu is on the PEN board of directors.
"We are disappointed by the Chinese government's decision to uphold Liu Xiaobo's sentence of 11 years in prison on the charge of 'inciting subversion of state power,'" said Jon M. Huntsman, U.S. ambassador to the People's Republic of China.
"We believe that he should not have been sentenced in the first place and should be released immediately. We have raised our concerns about Mr. Liu's detention repeatedly and at high levels, both in Beijing and in Washington, since he was taken into custody over a year ago," Huntsman said in a statement Thursday night.
"Mr. Liu has peacefully worked for the establishment of political openness and accountability in China. Persecution of individuals for the peaceful expression of political views is inconsistent with internationally recognized norms of human rights.
"We continue to call on the government of China to release him immediately and to respect the right of all citizens to peacefully express their political views and exercise internationally recognized freedoms," the ambassador said.
Liu's case was turned over to the prosecutor's office December 8 -- one year from the time Liu was detained.
"Liu has been engaged in agitation activities, such as spreading of rumors and defaming of the government, aimed at subversion of the state and overthrowing the socialism system in recent years," according to a police statement reported by China's state-run Xinhua news agency in December.
Liu co-authored Charter 08, "a declaration calling for political reform, greater human rights, and an end to one-party rule in China that has been signed by hundreds of individuals from all walks of life throughout the country," PEN says on its Web site. The group said Liu was arrested before the formal release of Charter 08.
The statement claimed Liu confessed to the charge during a preliminary police investigation.
Liu served as an adviser to student leaders during the demonstrations at Tiananmen Square in 1989. Along with three other intellectuals, he took part in hunger strikes there on June 2 of that year prior to the crackdown to show support for the flagging student protests.
He was arrested two days after the Tiananmen crackdown and was released in 1991. In May 1995, he was detained again for collecting signatures for a petition calling for human rights guarantees. He is also a former university lecturer and literary critic.
The U.S. government had previously called for Liu's release.
"The United States was deeply concerned to learn that ... Liu ... was found guilty of 'incitement to subvert state power,'" Mark Toner, acting State Department spokesman, said in December. "We call on the Government of China to release him immediately and to respect the rights of all Chinese citizens to peacefully express their political views."