BEIJING (REUTERS, AFP) - Nobel Peace Prize-winning activist Liu Xiaobo's liver cancer is beyond treatment by surgery, chemotherapy and radiotherapy, Liu's wife said in a video, as worries deepen among supporters over his treatment by the Chinese authorities.

Liu, 61, was jailed for 11 years in 2009 for "inciting subversion of state power" after he helped write a petition known as "Charter 08" calling for sweeping political reforms.

In December 2010, Liu was awarded the Nobel Peace Prize for his activism promoting human rights in China, causing Beijing to freeze diplomatic ties with Norway. China and Norway normalized ties in December last year.

Liu is currently being treated in a hospital in north China's Shenyang city for late-stage liver cancer, having been granted medical parole, his lawyer told Reuters on Monday.

A video of Liu's wife Liu Xia, who has been under effective house arrest since her husband won the Nobel Peace Prize, crying and talking about her husband's condition was shared online late on Monday.

"(They) cannot perform surgery, cannot perform radiotherapy, cannot perform chemotherapy," Liu Xia said in the video. She did not elaborate. It is unclear when the video was filmed.

A source close to the family confirmed the authenticity of the video and said Liu is being treated using targeted therapy. "They (the authorities) say his cancer has already spread too far for other treatments, but because we cannot meet the doctors treating him, we have no way to tell if this is true,"he said.

Liu and his wife wanted to return to Beijing for treatment but the authorities rejected their request, the source said. The prison bureau of Liaoning province said on Monday that Liu is being treated by eight "well-known tumour experts", but western politicians and rights activists have voiced concern about the quality of treatment.

"Even with the news today that Dr Liu has been released from prison for medical treatment, serious questions remain," USSenator Marco Rubio, co-chair of the Congressional-Executive Commission on China, said in a statement on Monday.

"I urge President Trump to seek Nobel Laureate Liu Xiaobo's immediate humanitarian transfer to the United States," he said.

The US embassy in Beijing said it was "working to gather more information" about Liu's legal and medical status after authorities confirmed his transfer from prison to a hospital in north-east China.

"We call on the Chinese authorities to not only release Mr Liu but also to allow his wife Ms Liu Xia out of house arrest," US embassy spokeswoman Mary Beth Polley told AFP. China should "provide them the protection and freedom such as freedom of movement and access to medical care of his choosing to which they are entitled under the Chinese constitution and legal system and international commitments," Polley said.

China's foreign ministry said on Monday it did not know about the circumstances of the case. China has in the past acknowledged problems of mistreatment in the criminal justice system and has repeatedly vowed to crack down to address them.

Wang Qiaoling, the activist wife of rights lawyers Li Heping, likened Liu's case to that of her husband and the other dozens of lawyers who say they suffer illnesses due to mistreatment in Beijing's most recent clampdown on dissent.

"Just as those captured in the 709 (crackdown) 'met with high blood pressure', we suspect Mr Liu Xiaobo 'met with liver cancer', and call for an independent third party medical organization to be involved," she said on Twitter.

Liu Xia, a poet, has been under house arrest since 2010, when her husband won the Nobel prize. She suffered a heart attack in 2014, when she was diagnosed with depression after years of detention, a rights group said at the time.

Nobel Committee: Strong regrets

The Nobel Committee said it was "delighted" to learn that Liu was finally freed, but that it "strongly regrets that it took serious illness before Chinese authorities were willing to release him from jail".

"Chinese authorities carry a heavy responsibility if Liu Xiaobo, because of his imprisonment, has been denied necessary medical treatment," it said.

Human Rights Watch and Amnesty International called on the authorities to ensure Liu's family can visit him. "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," Amnesty's China researcher Patrick Poon said.

Citing two other cases of critics who died in detention, Human Rights Watch's China director Sophie Richardson said the government "needs to be held to account for permitting yet another peaceful critic to fall gravely ill while unjustly detained." .

Bold petition

Liu is one of only three people to have won the Nobel award while jailed by their own government. China strongly condemned the prize as foreign interference in its internal affairs.

Diplomatic ties and trade talks between Beijing and Oslo were frozen, with China halting Norwegian salmon imports. Relations were only normalised last December.

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

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 3-4, 1989 when the military suppressed 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 for seeking the release of those jailed in the Tiananmen protests and for opposing the official verdict that their actions amounted to a counter-revolutionary rebellion.