In a hunt for Boko Haram leader Abubakar Shekau, soldiers of the Nigerian army on Friday conducted a search of a United Nations base in Maiduguri.

In what it termed ‘an unauthorized search’, Edward Kallon, the U.N. humanitarian coordinator for Nigeria, expressed "grave concern" on Friday over the military's actions in the north-eastern city.

The military confirmed the incident in a separate statement, saying the action is in line with ongoing search efforts.

Rumors have spread that Boko Haram leader Shekau may have been taking refuge in one of the U.N. buildings.

The U.N. says it has no information "regarding the reason or motivations for the unauthorized search."

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