A Tibetan nun imprisoned by Chinese authorities since her mid-teens for her political activities has been freed nine years early, a London-based monitoring group said on Thursday.

Ngawang Sangdrol, a nun aged in her mid-twenties, was freed nine years early for good behaviour, according to the Tibet Information Network (TIN).

Ngawang Sangdrol

Born 1977 Member of Garu nunnery in Lhasa First imprisoned 1992 Sentence extended for six years for singing songs Two further extensions for "counter-revolutionary crimes"

The move comes ahead of Chinese President Jiang Zemin's visit to US President George Bush's Texas ranch next week.

TIN director Thierry Dodin told BBC News Online the timing was significant.

"The Chinese side wants things to go smoothly," he said. "The US Government has been asking for the release of Ngawang Sangdrol for some time."

It was at least the seventh release of a Tibetan political prisoner since January.

Ngawang Sangdrol, born in 1977, was convicted in 1992. She is believed to be China's longest-serving female prisoner convicted of counterrevolution

Her release came a year after a prison report reduced her sentence by 18 months, saying she was showing "genuine repentance."

In July, a Tibetan scholar, Tanak Jigme Sangpo , believed to be China's longest-serving political prisoner, was released nine years early and flew to exile in the US.