According to local newspaper Dawn, the gunmen opened indiscriminate fire at the police mobile while it was patrolling the area.
The director of Police Quaidabad Mubarak Shah was among the four martyred police personnel.
Police suspected it was an act of targeted killing. An investigation into the cause of the incident is underway.
No group has claimed responsibility for the attack yet.
The attack came days after district Police officer of Qilla Abdullah, his security guard and driver were killed and more than 10 people, including five policemen, were wounded in the border town of Chaman on Monday.
