FACTBOX - China's restive Xinjiang region

REUTERS - Hundreds of Uighur Muslims crowded into at least one mosque in riot-stricken Urumqi on Friday after authorities relented on a decision to close mosques for the main day of prayer to minimize ethnic tensions.

Security forces have imposed control over Urumqi, but the prayers after midday will be a test of the government's ability to contain Uighur anger after Han Chinese, China's predominant ethnic group, attacked Uighur neighbourhoods on Tuesday.

Those attacks were in revenge for the deaths of 156 people in Uighur rioting on Sunday, the region's worst ethnic violence in decades.

Here are some facts about the region.

* Xinjiang, China's largest provincial-level administrative unit by area, covers one sixth of the country. It is relatively sparsely populated with around 20 million people.

* It is home to 8 million Uighurs, a Turkic, largely Islamic people who share linguistic and cultural bonds with Central Asia. Many resent the Han Chinese economic dominance in Xinjiang.

* The northern part of Xinjiang is economically dominated by the "bingtuan", military-run farms and businesses that predominantly employ Han Chinese settlers. In southern Xinjiang, where Uighurs are still the majority, China recently announced plans to raze the historic quarters of Kashgar, an oasis city.

* The Uighur language has been largely phased out of higher education and Uighurs are limited in their ability to travel independently to Mecca for the annual Haj. By contrast, China's central government has supported Islamic studies and Haj travel for the Hui, a Muslim people culturally akin to the Han.