Nearly one in five suicide bombers used by the Boko Haram terrorist group is children, with such attacks rising tenfold in one year, a shocking new report from the U.N. reveals.

The report from the U.N. Office for the Coordination of Humanitarian Affairs also states that more than 75 percent of the children used in Boko Haram suicide attacks are girls.

The news comes as Nigerian soldiers on Tuesday rescued the first of 219 Chibok schoolgirls who were kidnapped by the group in 2014.

Boko Haram, which operates in western Africa, carried out 44 children-involved suicide bombings in 2015, up from four the previous year.

“Over the past two years, nearly 1 in 5 suicide bombers was a child,” the report says.

In Niger, where Boko Haram attacks have increased since January, military offensives from regional multinational forces have pushed the extremists to border areas between Niger and Nigeria where they are attacking villages with little to no security.

In just one year, the number of displaced children in the region increased by more than 60 percent, from 800,000 to 1.3 million, the report states, citing figures from UNICEF.

Between January 2014 and February 2016, Cameroon was hit with the highest number of suicide attacks involving children at 21, followed by Nigeria at 17 and Chad with 2, according to the report.

The U.S., in April, announced nearly $40 million in new humanitarian assistance to those affected by Boko Haram violence.