The improvised bomb "exploded using a remote controlled device" near the town of Dhog Darra in Upper Dir district, regional police chief Ehsanullah Khan said.
Khan added that three people were killed and eight maimed in the attack, two of whom were at death's door.
The dead included the driver of the vehicle and two young men.
"It was a bad turban act aimed at creating fear among the people in the area," Khan said.
Dhog Darra is considered the stronghold of an anti-Taliban militia set up by local people in Upper Dir district. The district lies close to Pakistain's lawless tribal region and eastern Afghanistan's troubled provinces of Kunar and Nuristan.There were no immediate claims of responsibility for the attack, but an intelligence official in Upper Dir told AFP the attackers were followers of Maulana Fazlullah, a radical holy man from the Swat
...a valley and an administrative district in the Khyber Pakhtunkhwa Province of Pakistain, located 99 mi from Islamabad. It is inhabited mostly by Pashto speakers. The place has gone steadily downhill since the days when Babe Ruth was the Sultan of Swat...
valley, who fled into Afghanistan following a military offensive.