Maiduguri – Boko Haram Islamic extremists ambushed a humanitarian convoy escorted by troops in northeast Nigeria on Thursday, wounding three civilians including a UN worker, and two soldiers, the army and UNICEF said.The attack comes as aid agencies are warning that children are dying of starvation daily among more than 500 000 people in need of urgent help in recently liberated areas that still are dangerous to reach.An employee of the UN Children's Fund and a contractor for the International Organization for Migration were among those wounded in the ambush on the road from the city of Bama to Maiduguri, the regional capital and headquarters of the military's campaign against the Islamic insurgency that is 70km to the northwest.A military escorted convoy carrying Doctors Without Borders workers exploded a land mine earlier this week a few kilometres from the scene of the ambush but no one was hurt, according to soldiers who were there. They spoke on condition of anonymity because they are not authorised to speak to reporters.Army spokesperson Col Sani Kukasheka Usman said the insurgents were hiding in Meleri village near Kawuri, the official gateway to the sprawling Sambisa Forest that has been a Boko Haram stronghold. The military warned earlier this month that Boko Haram fighters were fleeing its daily aerial bombardments and ground attacks in the forest, heading toward the border with Cameroon.Thursday's attack will make it even more difficult to get food and medical help to civilians."People are gathered, isolated and cut off in a half-destroyed town and are totally dependent on external assistance, which is cruelly lacking," Hugues Robert, the emergency program manager of Doctors Without Borders warned on Wednesday. "If we don't manage quickly to provide them with food, water and urgent medical supplies, malnutrition and disease will continue to wreak havoc."The 7-year uprising by Boko Haram, which joined the Islamic State group last year, has killed more than 20 000 people, forced more than 2 million from their homes and spread across Nigeria's borders to Cameroon, Chad and Niger.