The first blast, which was of low intensity and was believed to have been caused by a grenade, occurred outside a polytechnic college on a key thoroughfare.

A suicide bomber struck about 10 minutes later when a group of policemen reached the spot, TV channels reported.

The suicide attacker detonated his explosives near a police van, killing several policemen instantly, officials said.

A contingent of paramilitary personnel were stationed in the polytechnic college as part of strict security measures put in place in Dera Ismail Khan for the Islamic month of Muharram, during which Pakistan has often witnessed sectarian violence in the past.

The town has in the past seen sectarian violence between Pakistan's majority Sunnis and minority Shiites.

President Asif Ali Zardari and Prime Minister Yousuf Raza Gilani strongly condemned the attacks. No group has yet claimed responsibility for the attack.