AFP PHOTO/DOCTORS WITHOUT BORDERS (MSF)*More than 100 people are said to have been injured
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.
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 told the BBC that, although it could not confirm the figure, up to 95 people had died.
AFP PHOTO/DOCTORS WITHOUT BORDERS (MSF)*MSF released photos of the aftermath of the air strike
"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 medical and surgical 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".
Army spokesman Maj-Gen Lucky Irabor said the jet's pilot had mistakenly believed he was attacking insurgents.
He said the mission had been ordered after reports of a gathering of Boko Haram fighters.
The general, who commands counter-insurgency operations in the north-east, said the air force would not deliberately target civilians and there would be an investigation.
A spokesman for the Nigerian president said the administration would offer help to the government of Borno state "in attending to this regrettable operational mistake".
Boko Haram has caused havoc in Africa's most populous country through a wave of bombings, assassinations and abductions.
It is fighting to overthrow the government and create an Islamic state.
Reuters news agency reports that the group has stepped up attacks in the past few weeks as the end of the rainy season enabled its fighters to move more easily in the bush.