Chinese authorities have suppressed protests over the jailhouse death of a revered Tibetan monk, and briefly detained two of his sisters for not signing his health record, rights groups said Thursday.

Police held the sisters of Tenzin Delek Rinpoche for "around 10 hours" on Wednesday, the US-based International Campaign for Tibet (ICT) cited local sources as saying.

Delek, 65, was 13 years into a life sentence for terrorism and separatism, imposed following a trial observers said was deeply flawed, when authorities announced news of his death at the weekend.

Delek was convicted of separatism and being involved in a bombing in a public square, but his supporters insisted he was innocent.

Authorities have so far refused to release Delek's body to his family or others in the Tibetan community, according to ICT, which said the circumstances of his death remained unclear.

Several protests in his hometown and in the southwestern city of Chengdu, where he was jailed, have taken place since his death was announced, according to ICT and other Tibetan rights groups.

Police opened fire when around 1,000 people gathered near government offices in Nyagchuka county this week to protest the death, injuring about 20 people, the British-based Free Tibet group said.

The US-funded Radio Free Asia also reported that police fired on the protesters, who were angry at a government decision to cremate his remains, rather than give him a traditional Tibetan burial.

ICT said his two sisters were detained after they "refused to sign a document that was described to them as being the health record of their brother".

"The sisters were apparently told that they would not be able to keep a copy, and the information on the document was not clear," it added.

One of the women apparently fainted in prison before the two were allowed to leave, it added.

AFP was unable to independently verify the reports of the protests, or contact authorities in charge of Delek's case.

Access to Tibetan regions is tightly controlled by the Chinese government and local media is barred from reporting issues the government deems sensitive.

China, which has ruled Tibet since 1951, has been accused of trying to wipe out its Buddhist-based culture through political and religious repression and large-scale immigration by Han Chinese, the country's ethnic majority.

China says Tibetans enjoy extensive freedoms and that it has brought economic growth to the region.

Tibetan spiritual leader the Dalai Lama fled Tibet after an abortive uprising in 1959 and established his government-in-exile in Dharamsala, India.

Delek became one of China's highest profile Tibetan prisoners when he was sentenced, which the United States and the European Union at the time condemned. Washington said it was "saddened" by his death.

Hollywood star and Tibetan rights activist Richard Gere expressed outrage over Delek's death on Tuesday.