Some of the 21 Chibok schoolgirls released by Boko Haram board a bus after their visit to President Muhammadu Buhari In Abuja, Nigeria October 19. (Afolabi Sotunde/Reuters)

The United Nations has negotiated the release this year of 876 children detained at a Nigerian army barracks because of suspicions of collaboration with the Boko Haram Islamic extremist group, the U.N. Children’s Fund announced Friday.

The agency fears that hundreds more children are still being held at the barracks in the northeastern city of Maiduguri, the UNICEF spokeswoman for Nigeria, Doune Porter, told the Associated Press.

Porter said many of the freed children were younger than 5, some still being breast-fed, and were detained because their parents were suspects. Nigeria’s military and police routinely lock up children along with parents suspected of a crime.

The detainees had been living in areas that were held by Boko Haram but then liberated, according to Manuel Fontaine, UNICEF’s director for West and Central Africa.

This is the first time the United Nations has reported negotiating the releases, though Nigeria’s army routinely reports how many minors are among the detainees it frees after interrogations that it says establish they have no links to Boko Haram.

In the biggest single release negotiated by UNICEF, 560 people were freed in September, including 430 children and some of their mothers, Porter said.

The detainees have been held in Maiduguri, the birthplace of Boko Haram and the home of the Nigerian army’s Giwa barracks. All the detainees at the barracks are held because of suspected support for Boko Haram.

The Associated Press has documented the deaths of thousands of detainees in unsanitary, overcrowded and inhumane conditions at Giwa barracks in recent years. Amnesty International has said 8,000 detainees died there between 2011 and 2015. This year, Amnesty called for the detention center’s closure, saying babies and children are among the many detainees dying from disease, hunger, dehydration and untreated gunshot wounds.

Brig. Gen. Rabe Abubakar, a spokesman for Nigeria’s Defense Ministry, has called the charges by the London-based human rights group “a distraction,” insisting that “our duty is to protect lives, and that is what we have been doing.”

It was not immediately clear how long the newly released children had been held. The army routinely detains civilians who live in areas that had been ruled by the insurgents on suspicion that they, too, might be linked to militant activities. But rights groups say there is no proper legal process for such civilians.

Fontaine said the conflict, which has killed thousands and displaced more than 2 million, has separated about 20,000 children from their parents, of which 5,000 had since been reunited with their families. But Boko Haram’s use of child suicide bombers, often girls, has contributed to fear in communities.

“Once we get children out, there is a major issue of stigmatization in the communities,” Fontaine said. “There is a sense that children who have been associated with Boko Haram for a while could be — and in some cases, we have some evidence, are — rejected by community and people around them.”

— Associated Press