URUMQI, China — Violent street battles killed at least 140 people and injured 828 others in the deadliest ethnic unrest to hit China's volatile western Xinjiang region in decades, and officials said today the death toll was expected to rise.

Security forces have clamped down on the city of Urumqi and set up checkpoints to catch any fleeing rioters, state media reported, after tensions between ethnic Muslim Uighur people and China's Han majority erupted into riots.

Rioters on Sunday overturned barricades, attacking vehicles and houses, and clashed violently with police, according to media and witness accounts. State television aired footage showing protesters attacking and kicking people on the ground. Other people, who appeared to be Han Chinese, sat dazed with blood pouring down their faces.

There was little immediate explanation for how so many people died. The government blamed Uighur exiles for stoking the unrest. Exile groups said the violence started only after police began violently cracking down on a peaceful protest.

About 1,000 to 3,000 people had gathered Sunday in the regional capital for the protest that apparently spun out of control. Accounts differed over what happened, but the violence seemed to have started when the crowd of protesters refused to disperse.

The official Xinhua News Agency reported hundreds of people were arrested. Mobile phone service provided by at least one company was cut today to stop people from organizing further action in Xinjiang.

The demonstrators had been demanding justice for two Uighurs killed last month during a fight with Han Chinese co-workers at a factory in southern China.

Tensions between Uighurs and the majority Han Chinese are never far from the surface in Xinjiang, China's vast Central Asian buffer province, where militant Uighurs have waged a sporadic, violent separatist campaign.

Uighurs make up the largest ethnic group in Xinjiang, but not in the capital of Urumqi, which has attracted large numbers of Han Chinese migrants. The city of 2.3 million is now about overwhelmingly Chinese — a source of frustration for native Uighurs.

Wu Nong, director of the news office of the Xinjiang provincial government, said more than 260 vehicles were attacked or set on fire in Sunday's unrest and 203 houses were damaged. She said 140 people were killed and 828 injured in the violence.

She did not say how many of the victims were Han or Uighurs.

Xinhua quoted regional Police Chief Liu Yaohua as saying several hundred people had been arrested in connection with the riot and police were searching for about 90 other "key suspects." He said checkpoints had been set up in the city and in neighboring Changji and Turpan prefectures to prevent the rioters from fleeing.