Police said the explosive materials were placed on the side of the road and detonated when the vehicle was passing by.
The police and security forces have started a search operation in the area.
The officials were heading back to DI Khan from Karachi where they had provided security for the Ashura processions.
Peshawar blast
Earlier on Saturday, two people including a police officer were injured in a roadside blast on Kohat Road in Peshawar, Express News reported on Saturday.
According to the Bomb Disposal Squad (BDS), four to five kilogrammes of explosives were used in the blast.
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