The blast, which destroyed the bus, occurred at Alizai Jozara near Hangu, a key city in Khyber-Pakhtunnkhwa province.
The minibus was heading to Kohat, another city located close to the restive tribal belt.
District police chief Abdur Rashid told PTI the blast was apparently caused by the explosion
of gas cylinders.
He did not rule out the possibility of terror attack and said a bomb disposal squad had been called in to investigate the incident.
"A bomber might have been present in the bus," another police official said.
Reports said the explosion apparently occurred after the bus collided with a pick-up truck though this could not be independently confirmed.
The injured were taken to a hospital in Hangu.
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