Dozens of worshippers were killed in an early morning bomb attack on a mosque on the outskirts of the restive Nigerian city of Maiduguri.

Dozens of worshippers were killed in an early morning bomb attack on a mosque on the outskirts of the restive Nigerian city of Maiduguri, residents and military sources said.

Two suicide bombers suspected to be Boko Haram members joined other worshippers in early morning prayers at a mosque at Umarari-Molai, some 6 kilometers from the city center, eye-witness Mohammed Sugum said.

A military source and rescue official from the national emergency agency said 21 corpses were taken from the scene.

"Evacuation and rescue work is still going on, but so far we have discovered 21 dead bodies," the relief worker told the agency on condition of anonymity.

Nobody has claimed responsibility.

The northeastern city of Maiduguri, epicenter of Nigeria’s six-year insurgency, has witnessed relative peace in recent months. The last bomb attack in the area occurred in January. There are still pockets of attacks in remote communities, though authorities claim to have decimated Boko Haram terrorist group.