China's western Xinjiang region has a long history of discord between China's authorities and the indigenous Uighur ethnic minority.
The Uighurs are Muslims. They regard themselves as culturally and ethnically close to Central Asian nations.
The region's economy has for centuries revolved around agriculture and trade, with towns such as Kashgar thriving as hubs along the famous Silk Road.
In the early part of the 20th Century, the Uighurs briefly declared independence. The region was brought under the complete control of communist China in 1949.
Xinjiang is officially designated an autonomous region within China, like Tibet to its south.
Activists say central government policies have gradually curtailed the Uighurs' religious, commercial and cultural activities. Beijing is accused of intensifying a crackdown after street protests in Xinjiang in the 1990s, and again in the run-up to the Beijing Olympics in 2008.
Over the past decade, many prominent Uighurs have been imprisoned or have sought asylum abroad after being accused of terrorism. Mass immigration of Han Chinese to Xinjiang had made Uighurs a minority in Xinjiang.
Beijing is accused of exaggerating the threat from Uighur separatists in order to justify repression in the region.
China's central government says Uighur militants are waging a violent campaign for an independent state by plotting bombings, sabotage and civic unrest.
Since the 9/11 attacks in the US, China has increasingly portrayed its Uighur separatists as auxiliaries of al-Qaeda, saying they have received training in Afghanistan. Little evidence has been produced in support of these claims.
More than 20 Uighurs were captured by the US military after its invasion of Afghanistan. They were imprisoned at Guantanamo Bay for years without being charged with any offence and most have now been resettled elsewhere.
Almost 200 people died in ethnic riots in Urumqi, the administrative capital of Xinjiang, in July 2009. One of the sparks for the violence seems to have been the deaths of two Uighurs in clashes with Han Chinese at a factory thousands of miles away in southern China.
The authorities blame Xinjiang separatists based outside China for the unrest, and they singled out exiled Uighur leader Rebiya Kadeer, saying she incited the violence. She denied any responsibility for the violence.
Uighur exiles say police fired indiscriminately on peaceful protests, leading to violence and deaths.
Xinjiang has received huge state investment in industrial and energy projects, and Beijing has been keen to highlight these as major steps forward. But many Uighurs complain that the Han are taking their jobs, and that their farmland has been confiscated for redevelopment.
The activities of local and foreign journalists are closely monitored by the state and there are few independent sources of news from the region.
However, occasional attacks on Chinese targets suggest Uighur separatism remains a potent and potentially violent force.