Beijing  - A small bomb hit a local government compound in the Ganzi Tibetan Autonomous Prefecture of south-western China's Sichuan province, state media reported Tuesday.

The official Xinhua news agency quoted local officials as saying the government compound of Ganzi's Bogexi township was hit just after midnight Monday by a "bomb thrown by terrorists."

No casualties were reported in the attack, which was still under investigation by local police, the agency said.

The brief report gave no further details and did not say if the attack was carried out by Tibetans or linked to recent anti-Chinese protests.

Tibetan exile groups reported several small protests in support of independence and the exiled Dalai Lama in the past few days, including at least one on Saturday's anniversary of rioting last year in Lhasa, the capital of the Tibet Autonomous Region.

Paramilitary police have sealed off almost all Tibetan areas of China to foreign journalists and tourists for more than one week while the government has tightened border security and cut off some text messaging and other mobile telephone services in Lhasa and other Tibetan areas.

"Tibet is virtually under undeclared martial law as the Chinese government has deployed massive paramilitary forces across the length of Tibet," the Tibetan government-in-exile said Sunday.

In Lhasa, where rioting broke out on March 14 last year, troops in full battle dress reportedly patrolled deserted streets in the city centre over the weekend.

The Chinese government said 18 civilians and one police officer died in last year's rioting that began in Lhasa.

The Tibetan government-in-exile said more than 200 people died in Lhasa and other Tibetan areas, most of them Tibetans shot by Chinese soldiers. (dpa)