PESHAWAR, Pakistan — A government official says a suicide bomber killed four people at a mosque serving as a headquarters for a militant group in northwest Pakistan.

Official Sadiq Khan says five people were wounded in the afternoon attack today in Tirah village in Khyber tribal area.

It was unclear what the motivation was behind the attack.

Khan says the mosque was a headquarters for Ansarul Islam, a militant group. The group is a rival to another militant outfit in the area known as Lashkar-e-Islam.

Khan says the bomber tried to enter the mosque but blew himself up at the doorstep.

Al-Qaida, Taliban and other militants are prolific in northwest Pakistan, especially in the lawless tribal regions bordering Afghanistan.