Some 15,000 people have been killed and more than two million displaced during a seven-year insurgency by the Islamist militant group that has been pushed back to its stronghold in the northeast's vast Sambisa forest in the last few months.
The UN has called for military escorts for aid workers trying to reach areas affected by the crisis, which has been exacerbated by soaring food prices and scarce reserves from the last harvest.
The agency has said 400,000 children aged under five would suffer from severe acute malnutrition in those states, which have been worst hit by the insurgency, and more than four million people faced severe food shortages in the region.
UNICEF also said it had increased the sum sought in its humanitarian appeal to help malnourished children in the region, where food supplies are close to running out, to $115 million - more than double the previous amount of $55 million.
