BEIJING, CHINA - Chinese authorities arrested a university economics professor in Beijing after he posted reports about the riots in Xinjiang on his website, an international media watchdog said Thursday.

Ilham Tohti, an ethnic Uighur, was arrested after Xinjiang authorities named his blog 'Uighur Online' on national television, calling it an outlet used to organise Sunday's protests in Urumqi, Reporters Without Borders said.

"The crackdown is not limited to Xinjiang," the media rights group said in a statement. "The authorities have arrested an independent writer who was just posting reports on his blog."

The Public Security Bureau would not confirm the arrest when contacted by AFP.

Officials at Minzu University of China in Beijing, where he teaches, were not immediately available for comment.

Authorities had previously pressured Tohti to stop posting in March and June, the statement said.

The Public Security Bureau warned him last month his postings exploring relations between ethnic Han Chinese and Uighurs, the ethnic majority in the Xinjiang region, violated the law, the statement said.

"Under the laws in force in China, certain subjects of conversation cannot be tolerated," the statement said, quoting a notice Tohti received.

Tohti's Chinese-language website, www.uighurbiz.net, was inaccessible in China on Thursday afternoon, joining Twitter, Facebook, YouTube and a range of sites that were blocked after providing independent updates on the riots.

Chinese authorities say at least 156 people were killed in riots following a protest in Urumqi Sunday. Sporadic violence continued in the city through Wednesday.