China clamped down on the Internet in the capital of China's northwestern region of Xinjiang on Monday, in the hope of stemming the flow of information about ethnic unrest which left 140 people dead.

The government has blamed Sunday's riots in Urumqi -- the deadliest unrest since the 1989 military crackdown on the Tiananmen pro-democracy demonstrations -- on exiled Muslim separatists.

Some residents in Urumqi, Xinjiang's regional capital, said they had been told there would be no Internet access for 48 hours.

Since yesterday evening I haven't been able to get online, store owner Han Zhenyu told Reuters by telephone.

No Internet here. Friends said they cannot log on, either, said a mobile phone seller who gave only his surname, Zhang.

The websites of the Urumqi city and Xinjiang regional governments were also down.

But the government appears to have thrown the net even wider, with users in capital Beijing and financial hub Shanghai complaining social networking site Twitter has also been blocked.

Fanfou.com, a domestic competitor of Twitter, was still accessible, though searches for key words such as Urumqi, Xinjiang and Uighur gave no results.

China has previously shut down communications in parts of Tibet, where ethnic unrest had erupted or was feared, and ahead of the 20th anniversary of the Tiananmen crackdown, as the government seeks to control the release of news through only official state media.

Yet in China, where a computer-savvy youth has embraced the Internet with enthusiasm, the government has not been able to control all the information seeping out of Xinjiang.

The incident has largely subsided, but armored cars were still in town this morning, one user, who said he was in Urumqi, wrote on Fanfou.com.

Several popular sites showed images claiming to be from the riots -- including one of a badly-mutilated body whose head had been almost hacked off.

Reuters has not been able to verify the authenticity of the pictures, many of which, like the one of the dead body, were removed after only a short time on the Internet.

Still, other Internet users took to the Web to express their anger over the riots.

Resolutely smash the splitist forces and terrorists! wrote on person on sina.com.cn, underneath a news report showing pictures of palls of black smoke enveloping Urumqi.

Yet the censor has also been working fast to remove most of the comments about the violence in Xinjiang, apparently to prevent ethnic hatred from spreading or Internet users questioning government policies toward regions populated by ethnic minorities.

By early afternoon, the bulletin board on Shanghai site pchome.net had numerous comments about the unrest, but they all vanished a few hours later, and replaced with the line: This posting does not exist.

(Additional reporting by Emma Graham-Harrison and Yu Le in Beijing; Editing by Benjamin Kang Lim and Sanjeev Miglani)

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