The small, densely packed camp includes people living in an old schoolhouse, mud-brick homes and other structures, some of which were smashed in the bombing, said Hugues Robert, the Nigeria program manager for Doctors Without Borders.

The bombing struck the camp early Tuesday afternoon, said Mr. Robert, who has been in touch with his team in Rann. The camp has been largely inaccessible for months, he said, and the charity’s workers had reached Rann for the first time only in December. Workers had returned on Saturday to establish a malnutrition screening clinic.

On Tuesday, that clinic was converted into a triage center as the wounded victims of the bombing, some with grievous injuries, jammed under the tents, lying in the soil to await treatment from the small number of medical professionals there, who were equipped to treat hunger, not blast wounds.

Darkness had fallen by the time more help arrived, and it seemed impossible to evacuate anyone before Wednesday, Mr. Robert said. “It’s really chaotic,” he said. “A lot of people won’t survive the night.”

Rann is known as a hotbed of Boko Haram activity. The military had cleared the area of militants just this spring, stranding 3,000 people without food or water, according to local news reports. But with the end of a rainy season that had limited mobility, Boko Haram has regained a foothold. Late last month, a military post near Rann was attacked in a battle that lasted three hours, an indication of the strength and firepower of militants in the area.

Before the bombing on Tuesday, the Nigerian military had been informed that fighters were amassing to attack a military post nearby, according to a Western diplomat who requested anonymity in talking about security issues. Armed with geographic coordinates of where they thought the fighters were assembled, the air force launched the bombing strike but hit the camp in error.