The Nigerian army on Thursday released 25 children after clearing them of suspected ties with armed groups in the country's restive northeast region, the United Nations Chindren's Fund said.

Nigeria has been dogged by a jihadist war for more than a decade, killing over 30,000 people and forcing millions others to flee their homes.

UNICEF said 23 boys and two girls were freed by the Nigerian army and handed to authorities in Borno State.

"These are children taken away from their families and communities, deprived of their childhood, education, health-care, and of the chance to grow up in a safe and enabling environment," said UNICEF Nigeria Acting Representative Pernille Ironside.

The UN agency said the children would be given access to medical support, education and vocational training.

The release comes against the backdrop of widely reported cases of young people being held captive in Nigeria in differing circumstances.

In May, a regional militia allied with government forces freed almost 900 children it had used in the war against Islamist insurgents.

Earlier this week police in Lagos, the commercial capital, said they had freed 19 women and girls who had mostly been abducted and made pregnant by captors planning to sell their babies.