More than 150 militants stormed the central prison outside the restive northwestern town ofBannubordering the tribal regions where militants are active.
The attack started at around1:00 amand continued for two hours, with militants in cars and pick-up trucks shooting and lobbing grenades to force their way into the prison, a senior security official told AFP.
"Some 400 prisoners, including some hardcore militants, have escaped during the attack," the official said.
"Preliminary information suggests that there were some 944 prisoners in the jail according to the tally late Saturday," he said.
A large number of militants had recently been moved to the jail from neighbouring Kohat and Lakki Marwat prisons, which are being converted into internment centres to rehabilitate former insurgents, the official said.
"There was an attack on the central jail and some prisoners escaped," senior Bannu police official Iftikhar Khan told AFP.
"At least three police officials were wounded in the attack," he said.
The attackers outnumbered the security forces at the prison and militants fled before reinforcements reached the jail.
Shafiq Ahmed, another police official said that security forces had imposed a cordon and a search operation was launched in the area.
"We have arrested four of the escaped prisoners," Ahmed told AFP.
Copyright AFP (Agence France-Presse), 2012