Liu Xiaobo, China's jailed Nobel peace prize laureate, has been granted medical parole after being diagnosed with terminal liver cancer last month, his lawyer says.

Liu, who has about three years of his 11-year sentence to serve, had the diagnosis on May 23 and was released a few days later, his lawyer Mo Shaoping told AFP new agency.

Liu, 61, was being treated at a hospital in the northeastern city of Shenyang.

"He has no special plans. He is just receiving medical treatment for his illness," Mo said.

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The democracy campaigner was sentenced in 2009 for "subversion" after spearheading a bold petition for democratic reforms.

He was awarded the Nobel prize a year later and was represented by an empty chair at the ceremony in Oslo.

Supporters voiced concerns about his health and criticised the way he was treated by Chinese authorities.

"Adding injury to insult, Liu Xiaobo has been diagnosed with a grave illness in prison, where he should never have been put in the first place," Patrick Poon, China researcher at global rights group Amnesty International, told AFP.

Poon called on Chinese authorities to ensure Liu "receives adequate medical care, effective access to his family and that he and all others imprisoned solely for exercising their human rights are immediately and unconditionally released".

Su Yutong, a Chinese journalist and activist in exile in Germany since 2010, said she was "very shocked and saddened" that her friend had fallen ill in prison, and urged authorities to let him travel overseas for treatment.

Bold petition

Liu is one of only three people to have won the Nobel award while jailed by their own government.

China condemned his Nobel prize as unwanted foreign interference in its internal affairs, and refused to allow him to attend the ceremony in Oslo.

Diplomatic ties and trade talks between Norway and China were frozen after Liu was given the award, and Norway's salmon industry suffered as exports to China were halted.

Relations were only normalised in December 2016.

Asked about Liu's parole, Geng Shuang, China's foreign ministry spokesman, said: "I am not aware of the situation you're talking about."

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The international community has been calling for his release for years.

Liu was arrested in 2008 after co-writing Charter 08, a bold petition that called for the protection of basic human rights and the reform of China's one-party Communist system.

Charter 08, which was posted online, specifically demands the abolition of subversion as an offence in China's criminal code, the very crime for which Liu has been jailed.

His wife, Liu Xia, has been under house arrest since 2010. She suffered a heart attack in 2014, when she was diagnosed with depression after years of detention, a rights group said.

Tiananmen role

Liu is also known for his efforts to help negotiate the safe exit from Tiananmen Square of thousands of student demonstrators on the night of June 3, 1989, when the military quelled six weeks of protests in the heart of Beijing.

He was arrested immediately after the crackdown and released without charge in early 1991.

Liu was rearrested and served three years in a labour camp from 1996 to 1999 for seeking the release of those jailed in the Tiananmen protests and for opposing the government's verdict that they amounted to a counter-revolutionary rebellion.

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The holder of a doctorate in Chinese literature, Liu was once a professor at Beijing Normal University, but was banned from teaching at state institutions over his involvement in the 1989 demonstrations.

Although Liu was banned from publishing in China, many of his writings advocating greater democracy and respect for human rights appeared in Hong Kong and overseas Chinese publications.

PEN Hong Kong, an organisation of journalists and writers advocating freedom of expression worldwide, also called for his unconditional release on Monday.

"At a time when China wants to have a greater international role, it is only fitting that it should show humanity and compassion towards a man who has never committed any violent crime, but has dedicated his life to literature and free expression," it said on its website.

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Source: AFP news agency