Bauchi - Boko Haram camp exploded, killing 63 people in the northeast.
Witness Haruna Bukar says the civilians were patrolling when they came across the bag of metallic objects and carried them to the nearby town of Monguno, where they exploded on Tuesday.
He says many curious people had gathered to inspect the objects when they detonated.
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Boko Haram had taken control of a large swath of the northeast until a multinational force this year forced them out of towns and villages. Nigeria's military says the extremists are confined to the Sambisa Forest.
Bombings and hit-and-run attacks continue, however.