The moves were an apparent bid to stanch the flow of information out of Xinjiang province and to prevent further rioting there. Over 800 other people were injured and the official death toll is likely to rise, the state-run Xinhua news agency said.

The government actions added to long-standing efforts to control online discussion of sensitive topics, especially at times of crisis.

"They cut off the Internet to shut down communications," said Wu'er Kaixi, an ethnic Uighur who fled China after helping lead pro-democracy protests there twenty years ago. The Uighurs are a minority concentrated in Xinjiang province that China has struggled to assimilate.

Beijing did not want Internet users to upload pictures and videos like they did after deadly riots last year in Tibet, Wu'er said.

China locked down communications much faster this time, he said.

Twitter became inaccessible in China around 3 p.m. local time Monday, according to complaints posted by users on the site. Users of Twitter and similar Chinese sites had been posting messages about the riots through the services. The Chinese sites were not blocked on Monday afternoon.

Twitter and other foreign Web sites, including Flickr and Microsoft's Bing search engine, were blocked for several days last month. The period included the date when China brutally suppressed the 1989 protests that Wu'er helped lead, an anniversary the government hoped would pass quietly.

China's telecommunications operators also appeared to block Internet access in Urumqi, the provincial capital where the riots occurred.

Wu'er said he had to use his parents' landline to reach them in Xinjiang on Tuesday.

"I normally call them on Skype but you can't get through now because the Internet is off," he said.

An employee reached by phone at an Urumqi hotel said Internet access in the building had been down since Sunday evening. Broadband users elsewhere in the city were also unable to get online, he said, declining to give his surname. The hotel gets its broadband service from China Telecom, one of China's three state-owned operators, the man said.

One Twitter user posted what he said was an explanation of the Internet outage from the provincial branches of China Telecom and China Unicom. Service would remain down indefinitely to prevent growth of the riots, the message said.

Long-distance call service dropped for China Telecom landline customers in Xinjiang after the riots, the same user said.