The 15-day celebration, called Losar, is usually one of most festive times for Tibetans, but this year there has been an underground campaign to boycott celebrations in memory of those killed during the wave of protests in the region last year.

Chinese officials have been worried about the potential for unrest round other sensitive dates, including the 50th anniversary of the failed Tibetan uprising against the Beijing government that led the Dalai Lama to flee into exile on March 10 1959. Beijing has named March 28 “Serf Emancipation Day”, a new holiday to celebrate the 50th anniversary of the official dissolution of the Tibetan government that was led by the Dalai Lama.

Analysts say the pre-emptive security clampdown indicates Beijing's lack of confidence that it can predict and prevent protests.