Islamabad: A suicide bomber blew himself up outside a mosque in northwest Pakistan's restive Khyber tribal region on Friday, killing at least 23 militants from the banned Lashkar-e-Islam group and injuring over 20 others.

The attacker detonated his explosive vest near the gate of the mosque as the Lashkar-e-Islam militants were leaving after offering Friday prayers this afternoon, officials of the local political administration told the media.

The incident occurred in Nakai area of Tirah Valley, located near the border with Afghanistan.

The area is controlled by the Lashkar-e-Islam, which is led by a warlord named Mangal Bagh Afridi.

Another militant faction led by Tariq Afridi claimed responsibility for the attack.

Officials said they feared the death toll may rise as some of the injured were in serious condition.

The explosion damaged the mosque and nearby structures, occurred in the same area, where an earlier clash had killed eight security personnel and 23 militants.