Image copyright Reuters Image caption Liu Xiaobo was a key leader in the Tiananmen Square protests in 1989

China has invited medical experts from the US and Germany to help treat Chinese Nobel peace laureate Liu Xiaobo, who has terminal liver cancer.

Authorities in the north-eastern Shenyang city, where Mr Liu is being treated, said the decision was made at the request of his family.

Mr Liu was jailed for 11 years in 2009 on subversion charges for calling for greater democracy.

China's decision comes just days before a G20 meeting in Hamburg, Germany.

Diplomatic sources in Beijing say China has been nervous the issue might overshadow President Xi Jinping's appearance at the summit, Reuters reports.

Mr Liu, who was a key leader in the Tiananmen Square protests in 1989, won the Nobel peace prize in 2010.

His wife Liu Xia has been under house arrest since then - but she has never been charged.

Mr Liu was diagnosed with cancer in May, and later was released on medical parole to be treated by tumour experts in Shenyang's hospital.

Since he was moved from prison, international human rights groups and several Western diplomats, including from both Germany and the US, have called for the dissident to be allowed to leave the country for treatment.

The Nobel committee in Oslo has described Liu Xiaobo as "the foremost symbol" of the human rights struggle in China.

He was never allowed to collect his prize and was represented by an empty chair at the ceremony. The Chinese government was infuriated by the award and cut ties with Norway for several years.

Mr Liu has three years left to serve of his sentence for "inciting subversion" after drafting Charter 08 - which called for multi-party democracy and respect for human rights in China.

Amnesty International has said he should never have been jailed.