The United Nations grounded flights, which are used for humanitarian missions, for a day on Friday, and some other aid organizations in the city said they were locked down, with workers staying in their quarters.

“The humanitarian crisis in Nigeria’s northeast is one of the most severe in the world today,” Edward Kallon, the agency’s humanitarian coordinator for Nigeria, said in a statement. “I am extremely concerned that these actions could be detrimental to the critical work that is being carried out every day to support the most vulnerable in the region, and I call upon the government of Nigeria to provide clarification.”

On Friday afternoon, the Nigerian military released a statement saying that the raid had no specific target.

Soldiers have been raiding various areas inside and outside Maiduguri to search for bomb-making materials and insurgents and, acting on a tip, raided the area of the United Nations camp and 30 houses nearby, according to the military statement. The camp “did not carry a U.N. designation,” according to the statement from the military. No arrests were made during the raids.

“The command wishes to assure the general public that these operations are being conducted to safeguard lives and properties but not targeted at any individual or group,” the statement said.