Islamabad - Gunmen on Wednesday opened fire on a police vehicle in Pakistan's insurgency-hit Balochistan province, killing four law enforcers, including a senior officer, police said.

The attackers, riding a motorcycle, sprayed the pick-up truck with bullets on a main artery of Quetta, the provincial capital, when two officers along with three constables were moving towards a training school.

"Four policemen, including a deputy superintendent of police (DSP), were killed," a junior official, Mohammad Ali, said over the phone. The other DSP was critically injured, with a bullet wound in his head, Ali added.

No one immediately claimed responsibility for the attack.

Balochistan is Pakistan's largest but most sparsely populated province where ethnic Baloch tribesmen are waging a low-intensity insurgency, seeking greater autonomy and a fair share of profit on natural resources explored in the area. (dpa)