New York: Nigeria-based extremist group Boko Haram is increasingly using children in "suicide" attacks, a UNICEF report released on Tuesday said.
One of every five suicide bombers deployed by Boko Haram in the past two years has been a child, usually a girl, according to the report.
Boko Haram used 44 children in suicide attacks last year, compared with only four in 2014, The New York Times reported.
The youngest bomber so far was thought to be eight-years-old.
In April 2014, the group kidnapped nearly 300 girls from a school in Chibok, Nigeria.
Several dozen escaped early on, but most are still missing.
Intelligence officials believe they are being used as human shields for Boko Haram leaders hiding in the Sambisa forest.
According to the report, the overall number of suicide bombings increased from 32 in 2014 to 151 last year. In 2015, 89 attacks were carried out in Nigeria, 39 in Cameroon, 16 in Chad and seven in Niger.
Cameroon has had the highest number of attacks involving children, Unicef said.
Government and defence officials in Cameroon have said most of the attackers there have been girls ages 13 to 15.
People who have escaped Boko Haram have reported a systematic program for training women and girls to be bombers.
In the report, Unicef said it needed $97 million to provide vaccinations, schooling, drinking water, mental health aid and other assistance to families affected by Boko Haram.
Boko Haram was the deadliest terrorist organization in the world in 2014, according to the Global Terrorism Index.