Five policemen and two civilians were killed Sunday in a suspected suicide blast in D.I. Khan, a local government official said. The explosion, which also wounded 28 people, took place on a busy road in the centre of town, district coordination officer Syed Mohsin Shah told a foreign news agency. Police said they believed it could have been a suicide blast, and that the police were the intended target. Bomb disposal experts were combing the scene for evidence. Shah said the police had come to the scene to investigate a tiny explosion, when their vehicle was hit in a second blast. Dera Ismail Khan is on the edge of tribal areas bordering Afghanistan, where hundreds of extremists fled after the Taliban regime was ousted from power in Kabul in a US-led invasion in late 2001. The town has in the past been the scene of sectarian violence between Sunnis and Shiites. Muslims are currently observing the mourning month of Muharram, but the official said there had not been any Shiite processions taking place near the scene of the blast.