About 1,000 to 3,000 Uighur demonstrators had gathered Sunday in the regional capital for a 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 and checkpoints ringed the city to prevent rioters from escaping. Mobile phone service provided by at least one company was cut Monday to stop people from organizing further action in Xinjiang.

Internet access was blocked or unusually slow in Urumqi on Monday. Videos and text updates about the riots were removed from China-based social networking sites such as Youku, a YouTube-like video service, and Fanfou, a Chinese micro-blogging Web site similar to Twitter.

A Fanfou search for posts with the key word Urumqi turned up zero results while Twitter, which is hosted overseas, yielded hundreds of comments in Chinese and English. Major Chinese portals such as Sina.com, Sohu.com and 163.com relied solely on Xinhua for news of the event and turned off the comment function at the bottom of the stories so people could not publicly react.

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

Uighur activists and exiles 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 are backward and ungrateful for the economic development the Chinese have brought to the poor region.

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 shops 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 said several hundred people had been arrested in connection with the riot and police were searching for about 90 other "key suspects." It also quoted a local police chief as saying 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.