They also condemned the Chinese government for refusing the political prisoner’s wish to travel overseas for treatment.

US Secretary of State Rex Tillerson was among those urging the Chinese government to release Liu’s wife from house arrest and to leave the country.

The White House said President Donald Trump was deeply saddened to learn of the death of Liu.

Press Secretary Sean Spicer said in a brief statement, “The President’s heartfelt condolences go out to Liu Xiaobo’s wife, Liu Xia, and his family and friends.”

Liu, 61, was a literary critic and writer who came to prominence in 1989 after he encouraged pro-democracy students to leave Beijing’s Tiananmen Square rather than face down armed soldiers.

Liu was imprisoned four times, the most recently for co-writing a document circulated in 2008 that called for more freedom of expression, human rights and an independent judiciary in China.

He was in prison when the Norwegian Nobel Committee awarded him the Peace Prize in 2010 for his “long and non-violent struggle for fundamental human rights in China”.

Renee Xia, international director of Chinese Human Rights Defenders (CHRD) , a network she said Liu helped found, said the mood among her colleagues has been one of despair over his impending death and disappointment that leaders did not do more.

“When we spoke to each other people would start crying. There was this sense of, it was just a dark world,” Xia said.

“Where are the moral leaders? Where are the values of human rights and human dignity and freedom?”

Former US President George W. Bush praised Liu in a statement, calling him a courageous man who “never wavered in his quest to advance freedom and democracy”.