Ethnic tensions are high in Xinjiang, an autonomous region in Western China. Rioters clashed with police – the largest protests in China in two decades – in the region’s capital, Urumqi, on Sunday and the Chinese state news agency reported that 156 people were killed and more than 1,000 were injured. Over 1,400 people have been arrested in connection with the events.

The violence apparently erupted after Uighurs, an ethnic minority in China, began demonstrating against the government’s handling of an earlier brawl in Southern China between Uighurs and Han Chinese. On Sunday, a heavy security crackdown and communication clampdown – the central government crippled Internet service, blocked Twitter’s micro-blogs, purged search engines of unapproved references to the violence and saturated the Chinese media with the state-sanctioned story – quelled the violence and Urumqi experienced a tense calm on Monday. Riots spread to Kashgar on Monday but were quickly dispersed. Hundreds of protesters reportedly defied the police and returned to the streets on Tuesday.

Uighurs make up nearly half of Xinjiang’s population of 20 million and are largely Muslim. Han Chinese, however, constitute over 90 percent of China’s entire population. Fueling resentment among minorities, the government actively encourages Han migration into Xinjiang (and Tibet) to help solidify control over the restive area and develop the economy. “Millions of Han Chinese, the country’s dominant ethnic group, have migrated into Xinjiang over the past 60 years, prompting complaints that they dominate local politics, culture and commerce at the Uighurs’ expense.”

Beijing promptly blamed outside groups for instigating the unrest and accused the World Uighur Congress of masterminding the violence. “State media have already accused exile Uighur groups of organizing the violence, just as it blamed the Dalai Lama for last year’s violence in Tibet,” said Sophie Richardson, Asia advocacy director at Human Rights Watch. “In both cases no evidence was produced to support the claims.”

While noting that it is unclear what happened in Urumqi over the past few days, Human Rights Watch wrote that “in recent years, security forces in Xinjiang have systematically conflated peaceful dissent with violent activities, and manipulated the threat of terrorism to justify systemic human rights violations and curbs on religious and cultural expression.”

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Photo from David Gray/Reuters and clip from CNN.