Islamist fighters from Nigeria’s Boko Haram group have abducted more than 1,000 children in the northeast since 2013, the United Nations children’s agency UNICEF said on Friday.

The militants regularly took youngsters to spread fear and show power, the agency said on the eve of the fourth anniversary of the abduction of 276 schoolgirls from the town of Chibok, a case that triggered global outrage.

“Children in northeastern Nigeria continue to come under attack at a shocking scale,” said Mohamed Malick Fall, UNICEF’s Nigeria head.

The agency said it had documented more than 1,000 verified cases, the first time it had published an estimated tally. But the actual number could be much larger, it added.

It said it had interviewed one young woman, Khadija, now 17, who was abducted after a Boko Haram attack on her town, then locked in a room, forced to marry one of the fighters and repeatedly raped.

She became pregnant and “now lives with her young son in an IDP (displaced persons) camp, where she has struggled to integrate with the other women due to language barriers and the stigma of being a ‘Boko Haram wife’,” UNICEF said.

At least 2,295 teachers have been killed and more than 1,400 schools have been destroyed in the conflict, it added.