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 Monday 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 has been little information about 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. Thousands of 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 Monday 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. Liu also said the death toll was expected to rise. Uighur exiles condemned the crackdown. "We are extremely saddened by the heavy-handed use of force by the Chinese security forces against the peaceful demonstrators," said Alim Seytoff, vice president of the Washington, D.C.-based Uyghur American Association. "We ask the international community to condemn China's killing of innocent Uighurs. This is a very dark day in the history of the Uighur people," he said. The association, led by a former prominent Xinjiang businesswoman now living in America, Rebiya Kadeer, estimated that 1,000 to 3,000 people took part in the protest. Xinjiang Governor Nur Bekri said in a televised address early Monday that Uighur exiles led by Kadeer of caused the violence, saying, "Rebiya had phone conversations with people in China on July 5 in order to incite, and Web sites ... were used to orchestrate the incitement and spread propaganda." A government statement quoted by Xinhua said the violence was "a pre-empted, organized violent crime. It is instigated and directed from abroad and carried out by outlaws in the country." Seytoff dimissed the accusations. "It's common practice for the Chinese government to accuse Ms. Kadeer for any unrest" in Xinjiang, he said. The clashes Sunday in Urumqi echoed last year's unrest in Tibet, when a peaceful demonstration by monks in the capital of Lhasa erupted into riots that spread to surrounding areas, leaving at least 22 dead. The Chinese government accused Tibet's exiled spiritual leader, the Dalai Lama, of backing the violence - a charge he denied. Many Uighurs long for independence for Xinjiang, a sprawling region rich in minerals and oil that borders eight Central Asian nations. Critics say the millions of Han Chinese who have settled here in recent years are gradually squeezing the Turkic people out of their homeland. But many Chinese believe the Uighurs (pronounced WEE-gers) are backward and ungrateful for the economic development the Chinese have brought to the poor region. Adam Grode, an American Fulbright scholar studying in Urumqi, described a heavy police and military presence in the city Monday. "There are soldiers everywhere, police are at all the corners. Traffic has completely stopped but people are walking on the sidewalks," Grode said. He said authorities took him to the police station Monday morning after seeing him taking photographs from his apartment window. They deleted his photos, confiscated his passport and released him. They gave no reason for taking his passport but said it would be returned Tuesday. Seytoff said he had heard from two sources that at least two dozen people had been killed by gunfire or crushed by armored police vehicles just outside Xinjiang University. Wang Kui, an official with the Foreign Affairs Department at the university, said she aware of no such incident. She said no students from the university were among those killed or injured. "We are not allowing students to come and go because the situation is chaotic at the moment," Wang said. "All the students are at school, and we are taking care of them. But we are not clear about what's been going on outside." China Mobile phone service was suspended in the region "to help keep the peace and prevent the incident from spreading further," a customer service representative in Urumqi said. The woman would give only her surname, Yang. Previous mass protests quelled by armed forces became signal events for Xinjiang's separatist movement. In 1990, about 200 Uighurs shouting for holy war protested through Baren, a town near the Afghan border, resulting in violence that left at least two dozen people dead. In 1997, amid a wave of bombings and assassinations, a protest by several hundred Uighurs in the city of Yining against religious restrictions turned into an anti-Chinese uprising that left at least 10 dead. In both cases pro-independence groups said the death tolls were several times higher, and the government never conducted a public investigation into the events.