Updated

A U.N. humanitarian official says more than half a million children in the West African area wracked by Boko Haram extremists are so malnourished their lives could be endangered if they don't get aid.

Military campaigns have driven the Islamic extremist group from much of the territory it took during a seven-year uprising. But the U.N. says a crisis remains.

Toby Lanzer, the U.N.'s humanitarian coordinator for the region in and around northeast Nigeria, said Monday some adults in the area are too weak to walk, and some communities have lost all their toddlers.

The U.N. is launching a more than $1 billion appeal, saying about 11 million people need aid.

Nigerian President Muhammadu Buhari has accused the U.N. and aid agencies of exaggerating the crisis to seek donations.