Chinese authorities have released a Tibetan monk from prison six years after he was arrested on suspicion of passing on news of protests against the Beijing government in the tense region.

The monk, Ngakchung, is believed to be in poor health after serving his prison term, Radio Free Asia has reported.

"He was released on July 8, but it is difficult to learn any details about his health," Serthar Chime said, citing contacts in the region.

"We know for sure that his health was not good while he was detained, and that his eyesight is very weak," he said.

He noted, "Because of a recent protest by another monk in Serthar [in Chinese, Seda] county, lines of communication in the area are blocked."

RFA quoted sources saying the monk is suffering from impaired vision.

An informant of RFA's Tibetan Service said Ngakchung was released on July 8, but there were no details about his condition.

The informant said lines of communication in Serthar county are difficult because of an earlier protest by another monk.

Ngakchung had been accused of passing information concerning the movements of Tibetan protesters in 2008 to outside contacts.

That year, authorities arrested the monk and his two companions -his elder cousin Traphun and a monk named Gudrak - while doing an errand for the Larung Gar Buddhist Institute.

The latter two were immediately released, but the monk was held and later on, was tried and sentenced to prison.

On top of the prison term, Ngakchung's sentence also stipulated that he could not exercise his political rights in the year after he completes his imprisonment, according to the informant.

A day after Ngakchung's release, authorities took another monk into custody for staging a protest.

Police arrested Larung Gar monk Sherkyab, 20, on July 9 after held a lone protest in the main town of Serthar county.

The monk purportedly chanted slogans that demanded freedom in Tibet and the return of the exiled spiritual leader the Dalai Lama. He also threw leaflets in the air.

Demonstrations against Chinese rule in Tibet have  been sporadic in recent years after widespread protest in the Tibetan-populated areas swept the region in 2008.

At least 131 Tibetan monks have self-immolated in the past five years, setting themselves on fire while protesting against Beijing's oppressive rule.