He said that he would not leave prison if that meant he had to leave Tibet

John Kamm, activist

He was imprisoned again in 1964 for allegedly making comments about Chinese repression of Tibetans, and sentenced a third time in 1970 on charges of inciting his niece to escape to India and report Chinese atrocities to the Dalai Lama.

But it was in November 1983 that he began serving his longest sentence.

No remorse

Initially sentenced to 15 years for "spreading and inciting counterrevolutionary propaganda," his official sentencing papers state that he "has previously served prison terms... but has never seriously reconsidered his past counterrevolutionary crimes".

His sentence was then repeatedly increased as a result of his involvement in various protests during his prison term.

The most high profile of these was on 6 December 1991, during a visit by Swiss government officials to Drapchi prison.

The then 65-year-old Tanag led a protest during which he and other prisoners shouted slogans supporting the Dalai Lama and calling for an end to Chinese rule in Tibet.

The embarrassed Chinese authorities asked the delegation to leave and then Tanag was reportedly dragged to his room and beaten until he was numb and placed in solitary confinement for six weeks.

He was due to be finally released in September 2011 at the age of 85.

Failing health

But there have been serious concerns about Tanag's health for several years. Initially said by the Chinese authorities to be suffering from "hypertension", in 2000 China admitted that he had received treatment for cardiac disease.

The Chinese authorities now say that he has "illnesses associated with old age" but these are "not life-threatening," according to John Kamm, a San Francisco-based activist who helped negotiate the release.

Tibet Information Network says that Tanag has been offered medical parole several times over the past two years but he always refused because he was worried that he would be a burden to his relatives and had become used to being in prison.

He was also reportedly unhappy about China's emphasis that he should seek medical treatment abroad.

But when the authorities said he would be allowed to stay in Lhasa for treatment he finally agreed to leave Drapchi prison.