At least 56 people, mostly militants, were killed in separate incidents of violence, including a suicide bombing outside a mosque and a fierce clash between security forces and pro-Taliban terrorists, in northwest Pakistan's restive Khyber tribal region on Friday.

A suicide attacker detonated his explosive vest near the gate of a mosque in Nakai area of Tirah Valley, located close to the border with Afghanistan, as the Lashkar-e-Islam militants were leaving after offering Friday prayers, officials of the local political administration told the media.

At least 23 militants were killed and over 20 others injured, the officials said.

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.

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

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