ABUJA, Nigeria — A suicide bomber set off explosives on Tuesday during morning prayers in a small, crowded mosque in northeastern Nigeria in a deadly attack that comes amid a raft of similar assaults on rural communities in the region.

Othman Abubakar, a spokesman for the police in Adamawa State, where the attack took place, said at least 50 people had been killed. Late in the day Tuesday the national emergency management agency said it had confirmed 23 deaths. Other officials could not confirm the death toll but blamed Boko Haram for the blast.

President Muhammadu Buhari issued a statement calling the attack “very cruel and dastardly.”

Boko Haram, a radical Islamist group that has waged war for the past eight years in Nigeria and in neighboring countries, has dispatched suicide bombers in a wave of attacks in the past year on mosques, checkpoints, markets and even camps for some of the nearly two million people uprooted from their homes because of the conflict.

