The UN envoy for children and armed conflict welcomed the release of 833 children on Friday by a vigilante group in northeast Nigeria, Xinhua reported.
"This is an important development for boys and girls of northeast Nigeria whose lives have been deeply affected by violence and insecurity," said Virginia Gamba, special representative of the UN secretary-general for children and armed conflict.
She said the release of children by the Civilian Joint Task Force (CJTF) was the result of months of productive work and collaboration between a UN task force in Nigeria and the vigilante group.
"We expect more children to be separated from the CJTF soon," said Gamba in a press release.
Nigerian authorities will provide reintegration services to all released children, with support from the United Nations Children's Fund and partners.
"We have an opportunity to help these children heal and rebuild their lives," said Gamba. "I call on all those who can support this process to work with us to ensure they have access to the best possible services."
The CJTF was formed in 2013 to protect communities in northeast Nigeria and to support the country's security forces in the fight against Boko Haram.
After intervention of the United Nations, the CJTF agreed in September 2017 to end the recruitment of children and to release all children from their ranks.
While Friday's release of children is an important milestone for the protection of children in Nigeria, Gamba reiterated her concern that children in the country's northeast continue to be subjected to grave violations committed mainly by Boko Haram, said the press release.
During the first half of 2018, 37 children, the majority of whom were girls, were used as "human bombs" to harm civilians. During the same period, 349 children were killed or maimed, and another 140 children were abducted, it said.
Gamba is also concerned about children detained by the Nigerian authorities for their or their parents' alleged association with armed groups, it said.
She appealed to the Nigerian government to consider these children primarily as victims, with detention used as a last resort and for the shortest period of time.
She also called on the Nigerian government to adopt a protocol for the handover of children allegedly associated with armed groups to civilian child protection actors without delay.