Maj. Gen. Lucky Irabor, a Nigerian army commander, said during a news conference in Maiduguri that two soldiers were "affected" during the operation. He did not elaborate.
"There are casualties and wounded but the actual numbers," he said, "I am yet to get the numbers of casualties of civilians (who) were killed."
Nigerian President Muhammadu Buhari described the airstrike as "regrettable" in a statement on Twitter.
"I received with regret news that the Air Force, working to mop up BH (Boko Haram) insurgents, accidentally bombed a civilian community in Rann, Borno State," Buhari said in a tweet
. "I sympathize with the families of the dead, and with the injured."
Humanitarian organizations condemn attack
Doctors Without Borders condemned what it called a "large-scale attack on vulnerable people." It said at least 120 people were wounded in the airstrike. The independent medical humanitarian organization, which has teams in the area, said the airstrike was "shocking and unacceptable."
"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," said Jean-Clément Cabrol, Doctors Without Borders' director of operations.
The group tweeted
images of destroyed structures and the injured, including at least one badly wounded child.
Doctors Without Borders teams were providing first aid to the wounded at their facility in Rann, the group said. They were also preparing to treat patients evacuated from the refugee camp.
ICRC Africa said on Twitter that six Nigerian Red Cross staffers had been killed and 13 others wounded Tuesday. The six staffers were in Rann as part of a humanitarian operation bringing food to more than 25,000 displaced persons, according to the ICRC.
"We are deeply saddened by the loss of our six colleagues and shocked that an incident of this magnitude has occurred in a civilian area," Chief Bolaji Akpan Anani, president of the Nigerian Red Cross Society, said in a statement Wednesday.
Hours after Tuesday's airstrike, a surgical team from the ICRC was deployed to Rann, where it treated 100 patients. According to the ICRC, around 90 patients remain in Rann, with about half severely injured and in need of airlifting to Maiduguri.
The United Nations airlifted out eight Nigerian Red Cross workers following the airstrike.
"This is an unfortunate tragedy that befell people already suffering the effects of violence," Edward Kallon, the UN Nigeria resident and humanitarian coordinator, said in a statement
. Kallon added that the Nigerian army has deployed a medical team and "is working with humanitarian partners to ensure maximum support to the affected people."
Human Rights Watch issued a statement Wednesday calling for Nigeria to compensate the victims and their families.
"Even if there is no evidence of a willful attack on the camp, which would be a war crime, the camp was bombed indiscriminately, violating international humanitarian law," said Mausi Segun, a senior Nigeria researcher at Human Rights Watch. "Victims should not be denied redress merely because the government decided the bombing was accidental."
Letta Tayler, a senior terrorism and counterterrorism researcher at the rights group, shared a satellite image on Twitter, which she asserted showed the camp in Rann easily visible from the air -- packed with tents.
Displaced find home in Borno
The UN Office for the Coordination of Humanitarian Affairs said in a statement that Rann, which has only recently become accessible to humanitarian groups, is home to around 43,000 internally displaced people.
Borno, which borders Cameroon, Chad and Niger, is home to the highest population of refugees in Nigeria, the majority displaced by fighting between government troops and insurgents, according to the International Organization for Migration.
Of the roughly 1.8 million people displaced by conflict, 92% of them are housed in camps in Borno, Adamawa and Yobe states, that organization reported last month
Correction: An earlier version of this article incorrectly described a statement by a Nigerian commander about casualties. The commander, Maj. Gen. Lucky Irabor, said that two soldiers were affected. He did not say that two soldiers had died.