Chinese state media say at least four people were killed Monday when a group attacked a police station in the country's western Xinjiang region.

The official Xinhua news agency said the rioters attacked the police station in the city of Hotan, seizing hostages and setting the building on fire. It said additional police converged on the station and shot a number of attackers while freeing six hostages.

The agency said one policeman, a security guard and two hostages were killed. It said a number of hostages were taken to the hospital.

Xinjiang in the past has been the scene of violent clashes between ethnic Han Chinese and its native Uighur population. The Chinese government says almost 200 people were killed during ethnic rioting in the region in 2009.

Dolkun Isa, secretary of the World Uighur Congress, a rights group based in Germany, says in the past couple of weeks police have arrested several people in Hotan and other areas without giving a reason.

He said Monday the trouble began after several relatives of those arrested had gathered to demand that the local government release the detainees.

It is not possible to independently verify the claims of either side, because it is difficult for outsiders to visit Xinjiang, and the Chinese government has tight control on telecommunications in the region.

Uighurs, a Turkic-speaking community, have long complained that the Chinese government suppresses Muslim religious practices and has encouraged millions of ethnic Han Chinese to migrate to the region, pushing Uighurs out of jobs.

Beijing denies those allegations and says it has done much to improve Xinjiang's economy and protect the rights of minorities. In the past, Chinese authorities have blamed separatists for unrest in the region.