A Nigerian air force jet has mistakenly bombed a camp for displaced people near Rann in the north-east, killing up to 100 people and injuring dozens more.
Aid workers are among the dead, with the Red Cross saying six of its employees were killed.
The MSF aid agency said it was treating 120 injured people and appealed for help with medical evacuations.
President Muhammadu Buhari, whose army is fighting Boko Haram militants, expressed dismay and urged calm.
The attack took place near the border with Cameroon where the military is engaged in what it calls its final push against Boko Haram.
It is thought to be the first time Nigeria’s military has admitted to making such a mistake.
‘Shocking and unacceptable’
An official from the Borno state government, who was helping to co-ordinate the evacuation of the injured by helicopter, told the Associated Press that 100 people had been killed.
MSF said that, although it could not confirm the figure, up to 95 people had died.
“This large-scale attack on vulnerable people who have already fled from extreme violence is shocking and unacceptable,” said Dr Jean-Clement Cabrol, MSF director of operations.
“The safety of civilians must be respected. We are urgently calling on all parties to ensure the facilitation of medical evacuations by air or road for survivors who are in need of emergency care.”
MSF said it had teams in Cameroon and Chad ready to treat wounded patients.
Many of the casualties, it said, were believed to be displaced people who had fled from areas where Boko Haram had carried out attacks.
“We are in close contact with our teams, who are in shock following the event,” MSF spokesman Etienne l’Hermitte said.
Red Cross spokesman Jason Straziuso was quoted by AP as saying the agency’s dead employees had been “part of a team that had brought in desperately needed food for over 25,000 displaced persons”.
‘All in pain’
Gen Rabe Abubakar, a spokesman for the Nigerian military, said that some “remnants” of Boko Haram had been detected outside Rann and the military had acted to eliminate them.
After the military realised its mistake, they were “all in pain”, he said.
“However, in a military operation such as this, from time to time these things do occur,” he added. “Even though it was highly regretful, it was never intended.”
Gen Lucky Irabor, who commands counter-insurgency operations in the north-east, said there would be an investigation.
By Africafrique and agencies