Nigeria's military says Boko Haram Islamic extremists have ambushed a humanitarian convoy escorted by troops, wounding three civilians including a U.N. worker and two soldiers.

The attack comes as aid agencies are warning that children are dying of starvation daily among half a million people in need of urgent help in recently liberated areas that still are dangerous to reach.

The U.N. Children's Fund says a UNICEF employee and worker for the International Organization for Migration are among those wounded in Thursday's ambush on the road from the city of Bama, 70 kilometers (43.5 miles) southeast of the regional capital, Maiduguri.

A military escorted convoy carrying Doctors Without Borders workers narrowly escaped a land mine this week a few kilometers (miles) from the scene of the ambush.