Police in the riot-torn western Chinese city of Urumqi shot dead two members of the Uighur ethnic minority and injured a third on Monday, underscoring the fragility of the calm secured by tens of thousands of security forces.

The city government said police officers on patrol in the central Urumqi district of Tianshan had killed the two men to stop them from hurting another one. According to its account, three Uighurs, armed with knives and sticks, were chasing a fourth one. When they failed to react to warning shots, the officers shot them dead “according to the law”, the city government said.