Human rights groups have expressed concerns about reports of clashes in Tibet last week between Chinese police and Buddhist monks.
Thousands of police were deployed at monasteries in Lhasa, and scores of monks are said to have been arrested.
They were celebrating the award of a US congressional medal to the Dalai Lama.
China regards him as the leader of a separatist movement. Beijing was furious at the US decision to give him the medal - one of the highest honours.
Tight security measures had already been put into place in the capital Lhasa.
Police intervened when the monks in Drepung began decorating the quarters traditionally reserved for the Dalai Lama, the most important figure in Tibetan Buddhism.
Security forces sealed off the monastery and another nearby, and there are reports that the unrest there carried on for several days.
Human rights monitors in the Indian city of Dharamsala, where the Tibetan government in exile is based, said they were still trying to collate reports about exactly how many monks were taken away, and where to.
The incident shows how revered the Dalai Lama still is among Tibetan Buddhists, almost 50 years after he fled into exile into India.
It is a mark of how nervous the Chinese authorities are about his enduring influence that even possession of his photograph is banned.