The explosion occurred near the garrison town of Kohat, which is a key base for Pakistani troops battling Al-Qaeda and Taliban militants in the semi-autonomous tribal districts on the border with war-torn Afghanistan.
"Seven people were injured in the bomb blast," local police official Shafiq Khan told.
"It appears to be a sectarian attack as all the passengers in the van were Shiites," he said. The blast was caused by a crude, makeshift device, he said.
Another police official, requesting anonymity, said one of the wounded died in hospital and that three of the wounded were in a serious condition.
Northwest Pakistan is beset with militant violence led by Taliban fighters who fled over the border following the US-led invasion of Afghanistan.
Extremist attacks blamed on Taliban and Al-Qaeda-linked militants have killed more than 1,800 people across Pakistan since July 2007.
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