The blast triggered by a remote control took place in Dera Ismail Khan city which over the past few months has been hit by clashes between Shias and Sunnis and Taliban-related violence.
Two men, who were guarding a Shia lawyer were killed in the blast, police said.
Several persons, including the lawyer, were also injured in the explosion that occurred in the parking lot of the district court, they said.
No group claimed responsibility for the attack.
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