SHENYANG, China >> Nobel Peace Prize laureate Liu Xiaobo, China’s most prominent political prisoner, died today at a hospital in the country’s northeast, officials said. He was 61.

Liu had been transferred to the hospital after being diagnosed with advanced liver cancer in prison in May but remained under police custody. In an online announcement, the judicial bureau of the city of Shenyang said he died of multiple organ failure.

Liu was only the second Nobel Peace Prize winner to die in prison, a fact pointed to by human rights groups as an indication of the Chinese Communist Party’s increasingly hard line against its critics. The first, Carl von Ossietzky, died from tuberculosis in Germany in 1938 while serving a sentence for opposing Adolf Hitler’s Nazi regime.

“Hitler was wild and strong and thought he was right — but history proved he was wrong in imprisoning a Nobel Peace Prize winner,” said Mo Shaoping, an old friend and Liu’s former lawyer, adding that he was heartbroken by Liu’s death. “The authorities consider Liu Xiaobo guilty, but history will prove he is not.”

Liu’s supporters and foreign governments had urged China to allow him to receive treatment abroad, but Chinese authorities insisted he was receiving the best care possible for a disease that had spread throughout his body.

News of Liu’s death triggered an outpouring of dismay among his friends and supporters.

“There are only two words to describe how we feel right now: grief and fury,” family friend and activist Wu Yangwei, better known by his penname Ye Du, said by phone. “The only way we can grieve for Xiaobo and bring his soul some comfort is to work even harder to try to keep his influence alive.”

Liu was imprisoned for the first time in connection with the 1989 Tiananmen Square pro-democracy protests. He was awarded the Nobel Prize in 2010 while serving his fourth and final prison sentence, for inciting subversion by advocating sweeping political reforms and greater human rights in China.

“What I demanded of myself was this: whether as a person or as a writer, I would lead a life of honesty, responsibility, and dignity,” Liu wrote in “I Have No Enemies: My Final Statement,” which he had hoped to read out in court when being sentenced in 2009. He was not permitted to do so and received an 11-year prison sentence.

He came to prominence following the 1989 pro-democracy protests centered in Beijing’s Tiananmen Square, which he called the “major turning point” in his life. Liu had been a visiting scholar at Columbia University in New York but returned early to China in May 1989 to join the movement that was sweeping the country and which the Communist Party regarded as a grave challenge to its authority.

When the Chinese government sent troops and tanks into Beijing to quash the protests on the night of June 3-4, Liu persuaded some students to leave the square rather than face down the army. The military crackdown killed hundreds, possibly thousands, of people and heralded a more repressive era.

Liu became one of hundreds of Chinese imprisoned for crimes linked to the demonstrations. It was only the first of four stays in prisons owing to his ideology.

His final prison sentence was for co-authoring “Charter 08,” a document circulated in 2008 that called for more freedom of expression, human rights and an independent judiciary in China. Although Liu wasn’t the initiator, he was a prominent force behind it and already well known to the authorities.

The sentence only increased Liu’s prominence outside of his country.

In 2010, while Liu was serving his sentence in a prison in a small city in China’s northeast, he was awarded the Nobel Prize, with the Norwegian-based committee citing Liu’s “long and non-violent struggle for fundamental human rights in China.”

The award enraged China’s government, which condemned it as a political farce. Within days, Liu’s wife, artist and poet Liu Xia, was put under house arrest, despite not being convicted of any crime. China also punished Norway, even though its government has no say over the independent Nobel panel’s decisions. China suspended a bilateral trade deal and restricted imports of Norwegian salmon, and relations only resumed in 2017.

Dozens of Liu’s supporters were prevented from leaving the country to accept the award on his behalf. Instead, Liu’s absence at the prize-giving ceremony in Oslo, Norway, was marked by an empty chair. Another empty chair was for Liu Xia.

Liu was born on Dec. 28, 1955, in the northeastern city of Changchun, the son of a language and literature professor who was a committed party member. The middle child in a family of five boys, he was among the first students to attend Jilin University when college entrance examinations resumed following the chaotic 1966-76 Cultural Revolution.

Liu studied Chinese literature there and later moved to the capital, first as a graduate student and then as a lecturer at Beijing Normal University.

After spending nearly two years in detention following the Tiananmen crackdown, Liu was detained for the second time in 1995 after drafting a plea for political reform. Later that year, he was detained a third time after co-drafting “Opinion on Some Major Issues Concerning our Country Today.” That resulted in a three-year sentence to a labor camp, during which time he married Liu Xia. He is survived by his wife and by his son from his first marriage.

Released in 1999, he joined the international literary and human rights organization PEN and continued advocating for human rights and democracy.

Liu Xia’s brother was convicted on fraud charges and sentenced to 11 years’ imprisonment over a real estate dispute which supporters said was designed to further persecute Liu Xiaobo’s family over his actions.

Two years after Liu’s Nobel prize, a Chinese writer won the Nobel Prize for Literature, to the delight of Chinese authorities. Mo Yan is not a critic of the Communist Party, and after initially evading questions from reporters, he eventually said he wished for Liu Xiaobo’s freedom.

Other Nobel laureates were more outspoken. In 2012, an appeal by 134 Nobel laureates, including South African Archbishop Desmond Tutu, called the detentions of both Lius a violation of international law and urged their immediate release. Fellow PEN members such as Margaret Atwood and Salman Rushdie appealed for his release in a letter on June 29 after he was transferred from prison to the hospital.

Their appeal fell on deaf ears.

Associated Press writer Gillian Wong and researcher Fu Ting contributed to this report from Beijing.