(CNN) -- Former Czech President Vaclav Havel showed up at the Chinese Embassy in Prague Wednesday to protest the imprisonment of a Chinese dissident, the official Czech News Agency reported.
Havel, himself a former dissident jailed by his country's Communist regime in the 1970s and 1980s, was criticizing the 11-year prison sentence imposed on Chinese dissident Liu Xiaobo.
Havel and two fellow former dissidents wanted to hand a letter personally to a Chinese official in the Czech Republic, but no one opened the door at the embassy, forcing Havel to put the letter in the embassy's mailbox, the agency reported.
Liu is a co-author of Charter 08, which calls for greater political freedom in China. It is modeled on Charter 77, an anti-Communist manifesto launched by Havel and others 33 years ago Wednesday.
Havel chose the anniversary date specially to make the protest, he said.
Liu has been one of China's most prominent dissidents since the 1989 Tiananmen Square protest -- which came, coincidentally, only months before Czechoslovakia's Velvet Revolution toppled Communism there and ushered Havel into the presidency. Czechoslovakia split into two independent countries -- the Czech Republic and Slovakia -- in 1993.
Liu was sentenced last month to 11 years in prison for his role in a separate subversion case, his lawyer said December 25.
Attorney Shang Baojun said that Liu's political rights would be suspended for two years under the sentence. Shang said he was disappointed with the verdict and felt the sentence was harsher than he had expected.
Liu, a former university lecturer and literary critic, faced a possible 15-year jail sentence, amid growing international outrage over his year-long detention, according to media reports.
He was detained on December 8, 2008, and held under "residential surveillance" as police investigated the case, according to the PEN American Center, a U.S. literary and human rights organization. On June 23, 2009, he was arrested and charged with inciting subversion of state power, the organization said. Liu is on the PEN board of directors.
The case was turned over to the prosecutor's office on December 8, 2009 -- one year from the time Liu was detained.
Charter 08 is "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.
"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.
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.
The U.S. government called for Liu's release.
"The United States was deeply concerned to learn that ... Liu ... was found guilty of 'incitement to subvert state power,'" said Mark Toner, an acting State Department spokesman. "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."
CNN's John Vause contributed to this report.