Image copyright Courtesy of students for a free tibet

A prominent Tibetan monk has died in a Chinese prison after 13 years in jail, his family and rights groups say.

Tenzin Delek Rinpoche, 65, was serving a 20-year jail sentence on separatism and terror charges, after being convicted of involvement in a 2002 bomb attack in Chengdu.

Tenzin Delek had denied the charges, calling them politically motivated.

The US, EU and rights groups had criticised his sentence at the time and called for his release.

Police in the south-western Sichuan city of Chengdu, where Tenzin Delek was being held, informed his relatives of his death on Sunday, rights group Students for a Free Tibet said.

His cousin Geshe Nyima, who is based in India, told Reuters that the cause of his death was not clear.

Another rights group, Free Tibet, said that the monk's family had asked for the return of his body, but this was rejected by prison officials.

A member of the Public Security Bureau in Sichuan's Dazhu county confirmed Tenzin Delek's death to the AP news agency, but refused to provide further details.

Image copyright Courtesy of Free Tibet Image caption Tibetans held prayer services last year calling for Tenzin Delek's release, activist groups said

The monk was initially given a suspended death sentence in 2002. This was later commuted to life imprisonment, and then a 20-year jail sentence.

Another monk, Lobsang Dhondup, who had been charged alongside Tenzin Delek over the bombing, was executed in January 2003.

Rights groups have accused China of suppressing Tibetan culture and freedom of expression, and detaining monks who have expressed support for Tibet's exiled spiritual leader, the Dalai Lama.

However, the Chinese government says Tibet's economy has developed considerably under its rule, and that Tibetan communities enjoy a great deal of autonomy under a system of devolved government.

In 1959, after a failed anti-Chinese uprising, the 14th Dalai Lama fled Tibet and set up a government in exile in India.