Beijing's propaganda portrays the vast and remote western region of Xinjiang as a harmonious land of colourful, mostly Muslim Uighur natives and hard-working migrants prospering under Communist Party rule.

But two incidents last week, one of which left 35 people dead, are only the latest spasms of violence to call into question that idealised vision.

China's constitution proclaims that the country's dozens of minority groups are an integral and equal part of the national tapestry, but analysts say a system of ethnic labelling -- originally meant to promote minority rights -- is fuelling unrest.

Xinjiang saw some of its worst inter-ethnic violence in years on July 5, 2009, when around 200 people were killed in clashes between Uighurs and China's Han majority. The fourth anniversary of the incident comes on Friday, in the run-up to the Islamic holy month of Ramadan.

Some form of Chinese rule in Xinjiang, where the culture has religious and linguistic similarities to the Turkic-speaking countries of Central Asia, dates back centuries.

Relations between the central government and peripheral regions were once more fluid, but since the Communist Party gained power in 1949 rigidity has become the rule, and all Chinese must carry identity cards that prominently state their ethnicity.

The country's constitution emphasises the need "to combat big-ethnic chauvinism, mainly Han chauvinism, and also to combat local-ethnic chauvinism".

"The state will do its utmost to promote the common prosperity of all ethnic groups," it says.

While ethnic categorisation was meant to foster minority rights and status, in places such as Xinjiang it now serves to harden parochial rather than national identity, analysts say.

"They've shot themselves in the foot by having fixed ethnic identification," said Reza Hasmath, an Oxford University lecturer in Chinese politics who studies Uighur issues.

"By virtue of doing that, the party has actually solidified ethnic boundaries."

Xinjiang, a region more than four times the size of Japan, is rich in natural resources and government economic policies aimed at developing it have raised Uighur living standards.

But millions of Han migrants dominate the economy, with high-status and high-paying jobs such as banking, technical services and public management, Hasmath said, and Uighurs cannot compete because of the dominance of Han social networks.

"Uighurs are not comparing themselves to other Uighurs, they're comparing themselves to other Hans," he said. "If you see the Hans are doing better than Uighurs it's going to create a greater divide."

The result, he says, is that frustrated Uighurs increasingly take refuge in ethnic and religious consciousness.

"This is how radicalisation occurs over the generations," he said.

Perceived interference in religious practice and culture, and the fact education is increasingly carried out in Mandarin, serve to marginalise them further, experts say.

"In general, as in the case in Tibet, they are trying to Sinicise the Uighurs," said Willy Lam, a Chinese politics scholar at the Chinese University of Hong Kong.

The central government has repeatedly condemned last week's violence -- in which state media said "knife-wielding mobs" attacked police stations -- as "terrorism".

It says local and foreign extremists have colluded in recent years, and it has boosted security, vowing to crack down on attacks.

Lam said such labels were "just a means to try to justify the harsh measures and failure to promote real ethnic harmony and conduct a genuine dialogue with the religious and intellectual leaders in Xinjiang".

Uighurs, he said, are unhappy about increased surveillance, heavier police presence at mosques and strict controls of legitimate Muslim and cultural activities.

The unrest in Xinjiang has drawn the attention of foreign diplomats in China.

"We do believe that it is necessary to address the underlying causes of ethnic tensions in order to achieve lasting stability and prosperity," EU ambassador to China Markus Ederer told reporters earlier this week.

Some leading communist officials in the past have pushed for a softer line on ethnic issues, Lam said, including former party general secretary Hu Yaobang and Xi Zhongxun, the late father of current President Xi Jinping.

But there is no support now for that approach, he said.

Xinjiang's population is now 46 percent Uighur and 39 percent Han, official figures show. When the Communist Party came to power, the Han proportion was less than seven percent, according to researchers.

"If you look at the numbers, the percentage of the Uighurs amongst the total population of Xinjiang is getting smaller," Lam said. "So I think Beijing believes that at the end of the day the numbers are on their side."