ABUJA, Nigeria — At least 200 people, mostly women and children displaced by violence in northeastern Nigeria, were abducted by Islamic extremists while they were searching for firewood near the border with Chad, the United Nations office in Nigeria said late Wednesday.

The victims had left several displacement camps to look for firewood in Borno state’s Gamboru Ngala council area when they were ambushed and taken hostage, the U.N. said, in the latest attack in the conflict-hit region where frequent abductions and killings limit movement.

“The exact number of people abducted remains unknown but is estimated at over 200 people,” the U.N. humanitarian coordinator for Nigeria Mohamed Fall said in a statement about the attacks, which occurred several days ago but whose details are only emerging now because of limited access to information in the area.

“While an unspecified number of older women and children under 10 have reportedly been released, scores of IDs remain unaccounted for, according to protection partners," Fall added.

Locals blamed the attack on Islamic extremist rebels who launched an insurgency in Borno in 2009 seeking to establish their radical interpretation of Islamic law in the region. At least 35,000 people have been killed and more than 2 million displaced due to the violence by the militant Boko Haram group and a breakaway faction backed by the Islamic State group.

Many of those fleeing the violence are in displacement camps like the ones in Gamboru Ngala where security is limited to areas near the camp, leaving them either to starve in the camps — amid dwindling aid — or risk their safety in search of food.

The latest attack is a “stark reminder” that women and girls are worst hit by the conflict, Fall said as he called for the immediate release of the victims. “This act of violence against already traumatized citizens offends our common humanity,” he said.

Nigerian security forces fighting the insurgents are overstretched as they also battle dozens of armed groups attacking remote communities in other parts of the northern region. The crises have added to pressures on Nigeria's President Bola Tinubu, who was elected last year after promising to end the violence.