Islamabad, Jan. 29 (Reuters): A suicide bomber killed himself, a policeman and a passerby in northwestern Pakistan today after police stopped him at a checkpoint, a doctor and security officials said.

The blast, the third suicide attack in Pakistan since Friday, occurred as police were on high alert for sectarian attacks during Muharram this week. “The attacker refused to be checked and detonated his explosives,” said Aslam Khattak, a senior police official in the town of Dera Ismail Khan, where the blast occurred. Seven people were wounded, he said.

A doctor at the town’s main hospital said three people had been killed, including the bomber.

Security officials in Dera Ismail Khan said earlier six people were arrested late yesterday on suspicion of planning suicide attacks and explosives had been seized from the suspects.

In a separate incident today, 13 people were hurt when two rockets were fired outside a Shia religious centre in the northwestern town of Bannu, said Asif Gohar, a police official in the town, which is near Dera Ismail Khan.