Image copyright EPA Image caption Protests over the fate of Liu Xiaobo have been held in Hong Kong

Terminally ill Chinese Nobel peace laureate Liu Xiaobo has asked to be allowed to go abroad for liver cancer treatment, his friends say.

His wife has formally requested to leave China but it is not clear if the authorities will approve it, they add.

Mr Liu, 61, has been in hospital after gaining medical parole.

He was jailed in 2009 for "inciting subversion" after calling for multi-party democracy and respect for human rights in China.

Image copyright AFP Image caption Liu Xiaobo (left) and his wife Liu Xia - pictured here in Beijing in October 2002 - are reported to be desperate to leave China

A statement posted on Twitter by Germany-based activist Liao Yiwu bore the signature of Mr Liu's wife Liu Xia and said that she wanted to leave China with her husband and her brother, the South China Morning Post reported.

"It is their desperate wish to receive medical treatment overseas. This is genuine. Xiaobo says he would rather die in the West," Liao wrote.

Mr Liu was reported to have been moved to hospital in Shenyang, in Liaoning province, shortly after his cancer diagnosis about a month ago.

A recent statement from the government in Liaoning said that Mr Liu was being treated by eight tumour experts.

Chinese justice ministry officials insisted that his family was satisfied with his treatment, Reuters reported. But a video showing him expressing gratitude to doctors for his care was dismissed by his friends as propaganda.

The officials have argued that his fragile health means that he is too ill to travel abroad.

But foreign diplomats say Mr Liu and Liu Xia should not be isolated from the outside world and should have the freedom to receive overseas medical treatment.

The US on Tuesday called on China to give Mr Liu and his wife - who is under house arrest - "genuine freedom".

China's foreign ministry responded by warning foreign countries not to "use any so-called individual case to interfere in China's internal affairs".

Image copyright AFP Image caption Liu Xia (seen with lawyer Mo Shaoping, left) has been allowed only brief, intermittent visits to her husband

Mr Liu was awarded the Nobel Peace Prize in 2010, with the Nobel committee describing the jailed dissident as "the foremost symbol" of the human rights struggle in China.

He was not allowed to collect his prize and was represented at the awards ceremony by an empty chair. The government regards him as a criminal and was infuriated by the award.