A Nigerian military strike on a camp for internally displaced persons in northeast Nigeria has killed dozens of people, according to Doctors Without Borders.

Teams from the organization, also known as Médecins sans frontières, said in a statement that they've counted 52 dead and 120 wounded as a result of the strike on the camp in Rann. They're treating the injured and preparing to evacuate patients from the camp.

The bombing was accidental and happened during an air force mission targeting Boko Haram insurgents in restive Borno State, according to tweets from Nigerian President Muhammadu Buhari.

"This large-scale attack on vulnerable people who have already fled from extreme violence is shocking and unacceptable," Dr. Jean-Clément Cabrol, MSF director of operations, said in a statement. "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."

Photos from the camp released by MSF show rows of newly dug graves and stunned-looking, injured civilians waiting for treatment. Other civilians survey the damage and look through burned-out ruins. The organization adds that its teams are "in shock following the event."

The Nigerian air force has been intensively targeting the extremist organization in the northern area of the country. As NPR's Ofeibea Quist-Arcton has reported, up to 2.5 million people have been displaced from the fighting.

"This is the first time during Nigeria's three-year campaign against Boko Haram that the military has acknowledged a large number of civilians killed in a mistaken bombardment," according to The Washington Post. "It remains unclear how the military could have mistaken a camp with 25,000 displaced people for a terrorist enclave."

Buhari pledged the federal government's support "in dealing with the situation and attending the victims."

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