Chinese authorities have barred most journalists from Tibet, and foreign tourists have also been refused the special entry permits needed to enter the territory.

On Monday Tibetan activist groups reported that Chinese security forces had surrounded a Tibetan monastery in southwestern China after monks held a rally a week before the 50th anniversary of a failed uprising against Chinese rule.

The failure of the 1959 uprising led to the Dalai Lama, the Tibetan spiritual leader, fleeing into exile in India.

This month also sees the anniversary of last year's bloody protests in Lhasa and other Tibetan areas against Chinese rule.

Prayers banned

According to activists, the monks in China's Sichuan province, bordering Tibet, demonstrated close to where another monk set himself alight last week in protest against Chinese rule over the Himalayan region.

The US-based International Campaign for Tibet (ICT) said scores of monks at Aba prefecture's Sey monastery rallied after officials banned prayers during a Buddhist festival.

"Several hundred monks marched from the monastery after officials banned them from praying, calling to be allowed to celebrate the Monlam prayer festival and for authorities to release all Tibetan prisoners," the group said.

The Dalai Lama other exiles and rights groups have reported a large security build-up in Tibet and neighbouring areas with Tibetan populations ahead of the anniversary.

Tibet's government-in-exile based in the Indian city of Dharamsala, says Beijing's response to last year's unrest left 200 Tibetans dead.

China says police killed one "insurgent" and blamed Tibetan "rioters" for 21 deaths.