Suspected terrorists killed 16 policemen in China's northwest Xinjiang region on Monday, state press reported.
Following are key facts about Xinjiang and the alleged threat there:
GEOGRAPHY: The region's vast 1.6 million square kilometres (618,000 square miles) accounts for a sixth of China's territory and spans into Central Asia. It borders Afghanistan, the former Soviet republics of Tajikistan, Kyrgyzstan and Kazakhstan, as well as Russia to the north and the Pakistan- and Indian-controlled parts of Kashmir to the south.
POPULATION: 20 million, representing 47 ethnic groups. The largest group are the 8.3 million ethnic Uighurs -- a Turkic-speaking central Asian people. But the number of Han Chinese in the region has risen from six percent in 1949 to more than 40 percent now.
ALLEGED TERRORIST THREAT: Groups identifying themselves as the East Turkestan Islamic Movement (ETIM) and the Turkestan Islamic Party (TIP) want to establish an independent homeland for ethnic Uighurs. Some experts believe the two groups are one. Washington say ETIM militants have received training and funding from Al-Qaeda, although some analysts dispute that.
(Agencies)