Police opened fire and wounded four rioters "out of self defense" in Sunday's unrest that rocked the Tibetan-inhabited Aba County in southwestern China's Sichuan Province, police sources told Xinhua Thursday.

The rioters burnt down the police station in the county's Aba township, lunged policemen with knives, and wrestled to seize police weapons, an official with the local public security bureau said.

Police fired warning shots, but the rioters didn't stop their violent seizures and continued attacking officers, he said. "Police were forced to open fire out of self-defense," the official said.

The injured attackers ran away with other mobsters amid the chaos, and the local police are carrying out further investigation into their whereabouts, he said.

The mob destroyed 15 police vehicles and more than 20 office facilities, including computers and printers in the police dispatch, he added.

The unrest began on Sunday afternoon when a group of rioters, shouting slogans of "Tibet independence", carrying rocks and self-made petrol bombs, attacked government offices, including the county government office building, police stations, hospitals, schools, shops and markets.

They also torched several dozens of houses and shops, burnt about 1,100 vehicles, and beat civilians, police and government officials.

Reportedly, police and government officials were injured by the rioters, and the amount of damage is not available, according to the county government.

In the neighboring province of Gansu, the counties of Xiahe, Maqu, Luqu and Jone and the Hezuo City in the Gannan Tibetan Autonomous Prefecture in southern Gansu also witnessed similar unrest from Saturday onwards.

The riots both followed the unrest that broke out in Lhasa on March 14. Thirteen innocent civilians were killed in the riots which the government said were organized by the Dalai clique.

Aba county, which is under the Aba Tibetan-Qiang Autonomous Prefecture, is in northwest Sichuan and neighbors provinces of Qinghai and Gansu in the north. It is more than 200 kilometers from the provincial capital of Chengdu.

It has a population of 63,000, mainly Tibetan, and the county seat of Aba has about 10,000 residents.

(Xinhua News Agency, March 21, 2008)