Islamabad, Nov 1 (IANS) Four people, including three school children and a policeman, were killed and 15 others injured when a bomb went off in Pakistan's southwest Balochistan province on Friday morning, official sources said.

The incident happened in the Mastung district of the province, where a police vehicle was targeted by a bomb explosion, the sources told Xinhua on condition of anonymity.

"The primary target of the terrorists was the police vehicle, but as the explosion happened near a school, a school van which was passing by the police vehicle also got hit by the bomb," the sources added.

The injured people, including policemen and school children, were shifted to a nearby hospital.

Several vehicles, including the police vehicle and school van, were damaged in the attack.

No group has claimed responsibility for the attack yet.