China's official news agency say three officers have been killed in a knife attack on a security checkpoint in the country's restive western Xinjiang region.

The attack is the latest in an upsurge of violence in the mostly Muslim region that started shortly before the Olympic Games under way in Beijing.

The state-run Xinhua News Agency said an unknown number of attackers jumped from a vehicle at a road checkpoint in Yamanya town at about 9:00 a.m. and stabbed four security officers. Three died and the other was injured.

The attackers fled and were still at large, Xinhua said.

On Aug. 4, assailants killed 16 border police and injured 16 others in a truck and bomb attack. On Sunday, bomb-wielding assailants attacked government buildings and fought with police; 12 people died.