The vehicle was on its way from Peshawar to the Shia-dominated area of Parachinar when the bomb exploded near Sadda town in the tribal region of Kurram, senior administration official Mohammad Anis said.
"It was an IED (improvised explosive device) blast," he told AFP.
The van was badly damaged in the remote-controlled explosion and two male passengers were killed while 14 people, including five women and four children, were wounded, he said.
Another official requesting anonymity said the victims were from the Shia community. He said they were from three families who had jointly hired the vehicle to travel to Parachinar.
Last month gunmen disguised in military fatigues hauled 18 men off their buses and shot them dead in the northern Kohistan region. Sectarian violence has killed more than 4,000 people since the late 1980s.
Human rights groups have heavily criticised the government for failing to crack down on sectarian violence between the two sects.
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