Kano, Nigeria: The death toll from a botched Nigerian air strike against Boko Haram that hit a camp for displaced people has risen to 90, and could climb as high as 170, Doctors Without Borders said on Friday.

Most of the victims of Tuesday's strike in Rann in the restive northeast on Tuesday were women and children, said the medical charity, which has called the strike "shocking and unacceptable".

Meanwhile, security sources said Boko Haram fighters launched an attack on the town in the far north of Borno state on Thursday evening that left at least 14 Islamist fighters dead.

Nigeria's air force said it has set up a board of inquiry which will report its findings before February 2, but military commanders have already called the bombing a mistake.

Major General Lucky Irabor, who leads the counter-insurgency, blamed the "fog of war" and said the intended target was jihadists in the Kala-Balge area, of which Rann is part.

Boko Haram fighters have been pushed out of their camps in the Sambisa Forest area of southern Borno by a months' long offensive.

MSF said in a statement: "Around 90 people were killed when a Nigerian air force plane circled twice and dropped two bombs in the middle of the town of Rann.

There were "consistent reports from residents and community leaders" that as many as 170 were killed but MSF director-general Bruno Jochum said: "This figure needs to be confirmed.

"The victims of this horrifying event deserve a transparent account of what happened and the circumstances in which this attack took place."

- Rann attacked -

Humanitarian workers were distributing food to between 20,000 and 40,000 people living in makeshift shelters at the camp when the bombs struck.

MSF's Jochum said civilians were paying the price of a "merciless conflict" between government forces and Boko Haram, which has allied itself to the Islamic State group in Iraq and Syria.

At least 20,000 have been killed and more than 2.6 million made homeless since Boko Haram's insurgency began in 2009.

International aid agencies have condemned the bombing of civilians, who are facing extreme food shortages because of the conflict, as well as having lost their livelihoods and families.

One aid worker, who asked not to be identified, described the incident as "horrifying" and "a huge setback to humanitarian work in the northeast".

Rann only recently became accessible to aid agencies because of improved security but Thursday night's attack underlined the fragile peace in the remote region.

One member of the civilian vigilantes in Rann told AFP a convoy of Boko Haram fighters on four pick-up trucks and several motorbikes "invaded the town", firing heavy weapons.

"We surprised them because they thought there wasn't enough security following the accident in the camp (on Tuesday)," he said on condition of anonymity.

"They met stiff resistance from security forces and vigilantes. Fifteen (Boko Haram fighters) were killed, a pick-up truck was impounded and some of them were arrested."

A police source in nearby Gamboru-Ngala gave a similar account but said 14 Islamists were killed. Both said Boko Haram had moved into the area after their ouster from the Sambisa Forest.