BANNU, Pakistan - Police say gunmen armed with hand grenades have attacked an office of the security force's intelligence wing in northwest Pakistan, taking several hostages and reportedly killing at least one officer.

Police official Zeenatullah Khan says the gunmen stormed into the office in Bannu city Monday morning.

Khan says police have cordoned off the building and exchanged fire with the attackers. Reports coming to police from inside the building indicate one of the officers has been killed.

It's unclear whether the gunmen are Islamist militants.

Pakistani Taliban fighters broke into a prison in the city in April and freed close to 400 prisoners, including 20 who were considered dangerous insurgents.