Security forces in central Tibet have increased patrols and border vigilance in advance of a sensitive anniversary to guard against possible disruptions caused by followers of the Dalai Lama or by Western groups advocating Tibetan independence, according to state news agency reports Monday. Meanwhile, a police car and a fire engine were attacked with homemade explosives in a Tibetan area on Monday, but no one was wounded.

The announcement of the increased patrols came one day before the 50th anniversary of a failed Tibetan rebellion against Chinese rule. After the 1959 revolt was suppressed, the Dalai Lama fled into exile in India.

Last March, the police clamped down on a protest by Buddhist monks in Lhasa, the capital of the Tibet Autonomous Region, prompting many Tibetans to riot in the streets. The uprising quickly spread to other Tibetan areas of China, becoming the largest-scale Tibetan rebellion against Chinese rule in decades.

The Chinese government fears the same thing could happen again this year, and it has been flooding Tibetan regions across western China with troops and police officers, creating an unofficial state of martial law. Foreigners have been barred from many areas.