"Many wounded are lying on the ground. We have two policemen and two civilians killed," said a police officer in the town of
Television news channels said a suspected suicide bomber blew himself up when he was blocked from entering a guest house where Asfandyar Wali Khan, leader of the Awami National Party (ANP), was holding a meeting.
The ANP is an ethnic Pashtun party based in the northwest and forms part of the ruling coalition government.
The party is liberal-leaning and fiercely opposed to Islamist militants waging a bloody campaign against the government.
A top party official told the Geo television channel that Khan was safe.