Tibetan students in Beijing have staged a candle-light vigil in an expression of solidarity with an unprecedented wave of protests in Tibetan areas across China.
Security personnel prevented reporters from speaking to the students in what appeared to be a rare sit-in protest at Beijing's elite Central University for Nationalities.
Human rights groups reported that protests against Chinese rule spread Monday into an increasingly number of Tibetan communities.
Official Chinese media has not reported on protests beyond the Tibetan capital, Lhasa, and the government has prevented foreign journalists from verifying reports.
But rights groups outside China have published photos and eyewitness reports of what they said were Monday's protests in several Tibetan communities in Gansu, Qinghai and Sichuan province, as well as the Tibet Autonomous Region.
Chinese Foreign Ministry spokesman Liu Jianchao Monday told reporters that the government has evidence that exiled Tibetan spiritual leader the Dalai Lama was behind last week's protests in Lhasa.
Liu offered to share the evidence with the international community at an unknown future date.
Witnesses say Lhasa is under lock-down and that anyone who goes out on the streets without a permit will be arrested as a midnight (1600 UTC) deadline for protesters to turn themselves has passed.
Earlier Monday, Tibet's governor Qiangba Puncog (also known as Jampa Phuntsok) said those who surrendered before the deadline and provide information would be given leniency.
Troops are patrolling the streets and authorities are continuing a door to door search for those involved in last week's peaceful rally that turned violent.
China says rioters killed 13 innocent civilians during last week's protests in Lhasa, but Tibetan groups outside the country say at least 80 Tibetans were killed. No death toll figures have been confirmed.
Qiangba insists that Chinese authorities did not use deadly force against protesters in Tibet last week, a claim that is refuted by the accounts of foreign witnesses in the city and Tibetan exile groups.
China has controlled Tibet since 1951. Tibet's spiritual leader, the Dalai Lama, and thousands of his followers fled from Tibet to India in 1959, during a failed revolt against Chinese rule. China denounces the Dalai Lama as a crusader for independence, but he says he has campaigned for nothing more than true autonomy for his homeland.