The United Nations has accused the Islamist extremist group Boko Haram of "almost unimaginable" violence and brutality in Nigeria.
Stephen O'Brien, the UN humanitarian co-ordinator, said the militant group's actions had forced thousands to flee and left unprecedented numbers in need.
The UN estimates that more than nine million people in the region need humanitarian assistance.
Boko Haram has pledged allegiance to the so-called Islamic State.
Mr O'Brien told the UN Security Council that Nigeria was bearing "the brunt of the crisis", with Nigerians accounting for seven of the nine million people in need.
He said Boko Haram's "heinous, barbaric and unconscionable" violence had led to serious human rights violations in the country.
"From January to June 2016, more than 50 children have been coerced to carry out suicide bombings across the four countries," he said.
UN political chief Jeffrey Feltman said Boko Haram remained a threat to stability in the region, despite the group being pushed back from some areas.
Both men warned the council that the fight against the group was suffering from a lack of funding.
The militant group continues to target countries in the region, including Nigeria and Cameroon, with bomb and suicide attacks.
The UN's children's agency Unicef warned last week that almost 250,000 children in parts of Nigeria's Borno state, formerly controlled by Boko Haram, were suffering from severe malnutrition.
Boko Haram at a glance:
- Founded in 2002, initially focused on opposing Western-style education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009
- Thousands killed, mostly in north-eastern Nigeria, and hundreds abducted, including at least 200 schoolgirls
- Joined so-called Islamic State, now calls itself IS's "West African province"
- Seized large area in north-east, where it declared caliphate
- Regional force has now retaken most territory