Police in Pakistan say gunmen in the country's southwest have opened fire on a vehicle carrying police officers, killing four of them before fleeing.

Senior police officer Abdur Razzak Cheema says the attack took place Saturday in the city of Quetta, the provincial capital of Baluchistan.

No group immediately claimed responsibility, but suspicion fell on Baluch nationalists and domestic militants who have been blamed for previous attacks.

Pakistan's Baluchistan province has been the scene of a low-scale insurgency for years. Separatists there often attack police and paramilitary security forces to pressure the government into allocating more wealth from resources like natural gas and oil extracted from the province.

Baluchistan also has witnessed recent sectarian violence against the country's minority Shite Muslims.