A peaceful protest Sunday of about 1,000 to 3,000 people in the regional capital, Urumqi, apparently spun out of control, as rioters went on a rampage and clashed with police. The official Xinhua News Agency reported hundreds of people were arrested.
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.
The demonstrators who gathered Sunday had been demanding justice for two Uighurs killed last month during a fight with their Han Chinese co-workers at a factory in southern China. Accounts differed over what happened next in Urumqi, but the violence seemed to have started when a crowd of protesters refused to disperse.
Rioters 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.
Mobile phone service provided by at least one company was cut Monday to stop people from organizing further action in Xinjiang.
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. The overwhelming majority of Urumqi's 2.3 million people are Han Chinese.
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 also reported 140 people died and that the death toll "was still climbing."
Xinhua said several hundred people had been arrested in connection with the riot and police were searching for about 90 other "key suspects."
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 Uihgurs. 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 blamed Uighur exiles led by Kadeer of causing 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."
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.
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.
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 dimisseed the accusations. "It's common practice for the Chinese government to accuse Ms. Kadeer for any unrest" in Xinjiang, he said.
Seytoff also read a brief statement from Kadeer: "The real cause of the problem lies with the Chinese government's policies toward the Uighurs. It's not alleged instigation by me or some outside forces."
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 the Dalai Lama of orchestrating the violence — a charge he denied.
Many Uighurs yearn 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.
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.
Four Uighur detainees at the U.S. prison at Guantanamo Bay in Cuba were recently released and relocated to Bermuda despite Beijing's objections because U.S. officials have said they fear the men would be executed if they returned to China. Officials have also been trying to transfer 13 others to the Pacific nation of Palau.