A Tibetan scholar, believed to be the country's longest-serving political prisoner, has arrived in the United States after being freed by the Chinese authorities earlier this year.

(He is) as determined and intransigent as ever

Kate Saunders, Tibet Information Network

Former teacher Tanag Jigme Sangpo, who is 76, had been in prison for most of the past 40 years.

He flew to Washington DC over the weekend, where he is expected to receive medical checks.

His release in April on medical grounds followed a number of appeals by Western governments and human rights groups.

Frail

The London-based Tibet Information Network (TIN) said he was believed to be suffering from high blood pressure and coronary heart problems.

A spokeswoman for TIN, Kate Saunders, told BBC News Online Mr Tanag was initially "elated" to arrive in the US but quickly became extremely tired and withdrawn.

But she said it was the organisation's impression that Mr Tanag would continue to campaign for the emancipation of Tibet.

She said that accounts of Mr Tanag over the last few weeks and days suggested that he was "determined and intransigent as ever and nearly 40 years in prison do not seem to have dimmed his dream for an independent Tibet".

"The Chinese authorities have not succeeded in breaking his spirit."

The State Department in Washington has also welcomed the news.

"We are pleased China has taken this step," spokeswoman Brenda Greenberg said, saying several US administrations had pressed for his release over the years.

A lifetime in prison

Mr Tanag was jailed in 1983 for 15 years for spreading and inciting "counter-revolutionary propaganda".

But his sentence was extended twice after he shouted pro- independence slogans during visits to his prison by foreign dignitaries.

He also spent much of the 1960s and 70s in prison and labour camps for criticising Chinese rule.

Activist John Kamm, who was involved in the negotiations for Mr Tanag's release, said at the time he was freed that it was "another indication that the Chinese Government will eventually respond to international pressure".

China seized control of Tibet in 1950 - a move it describes as "peaceful liberation" and the Tibetan government-in-exile says was invasion.

Since January the Chinese authorities have released six Tibetans imprisoned for their pro-independence activities.

Figures given to John Kamm by the Chinese Government say there are currently 110 such prisoners in Tibet.