The U.N. children's agency warns that some 49,000 children will die of malnutrition in areas once cut off by northeastern Nigeria's Islamic extremist uprising if they don't get treatment.

UNICEF is calling for charities and donors to respond quickly to avert a tragedy in Borno state, where nearly a quarter of a million children are severely malnourished.

Most of the children are in areas that had been inaccessible before a multinational force liberated them from Boko Haram extremists earlier this year.

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The seven-year Boko Haram insurgency has killed more than 20,000 people in the region.

The UNICEF statement Tuesday says the agency has received less than half of the $55.5 million it appealed for earlier this year, and now the needs are even greater.