Nearly 1,000 protesters from a Muslim ethnic group rioted in China's far west, overturning barricades, attacking bystanders and clashing with police in violence that killed at least four people, including a policeman, state media and witnesses said.

Protesters, mostly from the Uighur ethnic group, set dozens of cars on fire and attacked buses in several hours of violence in the Xinjiang province city of Urumqi. The violence appeared to subside as the police and military presence intensified into the night, according to participants and witnesses. 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 sporadic, violent separatist campaign. The overwhelming majority of Urumqi's 2.3 million people are Han Chinese.

State television aired footage that appeared to show protesters attacking and kicking people on the ground. Other people 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. The protest started Sunday with demonstrators demanding an investigation into a fight between Uighurs and Han Chinese workers at a southern China factory last month. Accounts differed over what happened next in Xinjiang's capital of Urumqi, but the violence seemed to have started when a crowd of protesters - who started out peaceful - refused to disperse.

State media said at least 37 people - both Uighur and Han Chinese - were hospitalized with injuries. Adam Grode, an American Fulbright scholar studying in Urumqi, said he heard explosions and also saw a few people being carried off on stretchers and a Han Chinese man with blood on his shirt entering a hospital.

He said he saw police pushing people back with tear gas, fire hoses and batons, and protesters knocking over police barriers and smashing bus windows. "Every time the police showed some force, the people would jump the barriers and get back on the street. It was like a cat-and-mouse sort of game," said Grode, 26.

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. Restoration of service will depend on how the situation develops," said the woman who would give only her surname, Yang. Another provider, China Unicom, said there was no interruption of its service in Xinjiang.

The official Xinhua News Agency reported that "the situation was under control" by Monday morning and that police had shut down traffic in parts of the city as a precaution. Xinhua said at least four people were killed in the violence, in which the crowd attacked passers-by, burned or vandalized 30 buses and cars and interrupted traffic on some roads. The report said that 37 injured people had been treated at the Traditional Chinese Medicine Hospital in Urumqi, and quoted a hospital official who spoke on condition of anonymity as saying those admitted were both Han and Uighur. Xinjiang's government accused Uighur exiles led by a former businesswoman now living in America, Rebiya Kadeer, of fomenting the violence via the telephone and Internet. Xinjiang Governor Nur Bekri said in a televised address early Monday that "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." Kadeer's spokesman, Alim Seytoff, said by telephone from Washington, D.C., that the accusations were baseless. "It's common practice for the Chinese government to accuse Ms. Kadeer for any unrest in East Turkestan and His Holiness the Dalai Lama for any unrest in Tibet," he said.

Uighur rights groups and militants demanding an independent Xinjiang often refer to the sprawling region of deserts and mountains, which borders eight Central Asian nations, as "East Turkestan."

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. 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 demonstration started peacefully with more than 300 people staging a silent sit-down protest in People's Square in Urumqi to demand an investigation into the June 25 brawl at a toy factory in southern China, said Gulinisa Maimaiti, a 32-year-old employee of a foreign company who took part in the protest. Xinhua said two died in last month's factory melee in southern Guangdong province, others say the real figure was higher. Gulinisa said in a phone interview that the crowd grew to 1,000 people, and when they refused to disperse, police pinned protesters to the ground before taking 40 protesters away. Uighur separatists have waged a sporadic campaign for independence in recent decades, and the military, armed police and riot squads maintain a visible presence in the region. After a few years of relative calm, separatist violence picked up last year with attacks against border police and bombings of government buildings.

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.