At least 140 people have been killed in rioting in the capital of China's north-western region of Xinjiang. The Chinese government is blaming exiled Muslim separatists for the area's worst case of ethnic unrest in years.

Hundreds of rioters were arrested after rock-throwing Uighurs took to the streets of the regional capital on Sunday, some burning and smashing vehicles and confronting ranks of anti-riot police.

The unrest underscores the volatile ethnic tensions that have accompanied China's growing economic and political stake in its western frontiers.

A senior official swiftly delivered the government claim that the unrest was the work of extremist forces abroad, signalling a security crackdown in the strategic region near Pakistan and central Asia.

Police rounded up "several hundred" who participated in the violence, including more than 10 key players who fanned unrest.

The riot in Urumqi, a city of 2.3 million residents 3,270 km (2,050 miles) west of Beijing, followed a protest against government handling of a June clash between Han Chinese and Uighur factory workers in Shaoguan, southern China Two Uighurs were killed in the fighting.