The van was attacked near a jail at Timergara, the main city of Lower Dir district in Khyber Pakhtoonkhwa province.
A TV news channel reported that the van was targeted with a remote controlled explosive device.
The injured were taken to Timergara hospital. Later, one person in a critical condition was taken to Peshawar, the capital of Khyber Pakhtoonkhwa.
Reports said police fired in the air shortly after the blast. No group claimed responsibility for the attack.
Taliban militants are active in the area and have attacked security forces and political activists in Lower Dir district in the past.
Published 24 April 2010, 03:57 IST