Witnesses say Islamic extremists who hid their weapons inside a coffin shot and killed 13 people in a northeast Nigeria city.

The attack happened Friday in Maiduguri, the spiritual home of the extremist network Boko Haram. Witnesses told an Associated Press reporter that the attack appeared to be in retaliation for a local vigilante group pointing out Boko Haram members to the military there. They say eight Boko Haram fighters were killed in the attack.

A security official says soldiers and police killed another eight suspected Boko Haram members in a gunfight Thursday in the city. The official spoke on condition of anonymity as he was not authorized to speak to journalists. An AP reporter saw the corpses Saturday left in a ditch in the city.