Xinjiang, where at least 140 people have died in China’s worst riots since the Tiananmen Square massacre, is a vast area of desert and mountains, as distinct from eastern China in history, atmosphere and geography as Turkey is from Britain. Even the time is out of joint — while the clocks are required to display official Beijing time, for practical purposes Xinjiang is two hours’ behind, so that the streets are dark and deserted at eight in the morning and bright and alive with people at midnight.

Camels still trudge through the desert along the old Silk Route, and lumps of white jade are bought and sold in bazaars beneath the minarets of tiled mosques. The city of Urumqi, where Sunday’s riots took place, is a large and developed place with the air pollution, ugly construction and modern conveniences of many large Chinese cities. There, immigrant Han Chinese from the East outnumber the local Uighur people. But, as the events of the weekend demonstrate, tension and physical conflict between the two is never far from the surface.

The months preceding last year’s Olympic Games saw increasing activity by shadowy separatist organisations who seek to throw off the Government of communist China and establish the independent Islamic state of East Turkistan. Chinese authorities reported a series of terrorist plots, although there were doubts as to whether these were serious terrorist threats or were exaggerated by the Chinese authorities to justify intense security measures.

Then, just before the Games opened, 16 policemen were killed in a frenzied knife and bomb attack by two Uighurs in the city of Kashgar, followed by further deadly attacks in Kuqa and Yamanya. If the past few months have been without major incident, it is not because any of the core grievances of the people behind the attacks have been addressed.

As a people, the Uighurs look more like Afghans than ethnic Chinese. Ethnically, they are a Turkic race whose homeland is at the meeting point of Asia and Europe. The area now called Xinjiang was annexed by the Chinese Empire in the 19th century, although it briefly achieved independence before the Communist victory in China in 1949.

Separatist sentiment has always been present, but the stern censorship and political repression of the Chinese Government have prevented it from forming a large-scale organisation. Small groups operated in secret but only began to make their presence felt in the 1990s, when the liberation of the former Soviet republics and the increasing dominance of ethnic Chinese stirred a new sense of aspiration among many Uighurs.

In 1949 the Han Chinese had made up six per cent of Xinjiang’s people; today they represent 41 per cent in a population of 19 million, compared to 45 per cent Uighur. Many of them believe that the goal of the Chinese Communist Party, barely concealed, is the complete cultural, religious and linguistic assimilation of the Uighur people.

After the terrorist attacks of 11 September 2001, China identified itself as a victim of international terrorism and the Uighur separatist movement as its own al-Qaeda. Uighurs were captured in Afghanistan — four of them were released last month to Bermuda. The Chinese authorities, fearful of violence before the Olympics, announced a raid on a training camp run by the East Turkistan Islamic Movement in January last year. Human rights organisations say that the Chinese anti-terror campaign has blurred the lines between genuine men of violence and those who peacefully support independence.

China pays lip service to freedom of religion for Uighurs, but only under its own terms. Imams must be licensed by the state. Public servants, including teachers, are barred from worshipping at mosques on pain of dismissal. Most resented of all, no one under 18 is allowed to worship or to receive religious instruction.

This goes further even than the control exerted over Tibetan Buddhism — to many Uighurs it represents a deliberate attempt to snuff out their religion over the course of a few generations by ensuring that young people grow up fully secularised. There is a small overseas diaspora, but compared to the Tibetan cause the Uighurs have few influential international friends. The chances of realising the dream of an independent “Uighurstan” are slight to non-existent. But, as the latest events have showed, it is a dream that will not die peacefully.

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