In a statement, it says that 106 girls were among the 894 children released by the pro-government Civilian Joint Task Force (CJTF) "as part of its commitment to end and prevent the recruitment and use of children".

The CJTF supports the army in its fight against Boko Haram.

“Any commitment for children that is matched with action is a step in the right direction for the protection of children’s rights and must be recognised and encouraged,” said Mohamed Fall from the UN's children's agency, Unicef.

“Children of north-east Nigeria have borne the brunt of this conflict," he added.

"They have been used by armed groups in combatant and non-combatant roles and witnessed death, killing and violence."

The UN says that those freed will take part in reintegration programmes to help ease back into civilian life.