An investigation found that the air force saw people massing in the area on satellite footage, assumed they were Boko Haram Islamist militants and launched the assault, the military said in a statement. Rann is in Nigeria’s Borno state, the heart of an eight-year-old insurgency by Boko Haram fighters who have killed thousands in their bid to carve out an Islamist caliphate.

“The main reason that caused the unfortunate air strike near the IDP (internally displaced person) camp at Rann, was lack of appropriate marking of the area,” the military statement said.

“Hitherto, people were not expected to amass at that location. Furthermore, the location was not reflected in the operational map as a humanitarian base.” All humanitarian sites should be marked on military maps in future, the investigators said.