"These children are victims, not perpetrators," said Manuel Fontaine, UNICEF's regional director for West and Central Africa, following the release of a report about the use of child bombers by Boko Haram.

Compared to 2014, in which four children had carried out suicide attacks, the number grew to 44 a year later.

Broken down by country, UNICEF reported that 21 children in Nigeria and 21 in Cameroon were used as suicide attackers in Nigeria, with a further two involved in bombings in Chad. The UN agency said the deadly strategy meant that many communities now see children as a threat.

Communities left in fear

"The calculated use of children who may have been coerced into carrying bombs has created an atmosphere of fear and suspicion that has devastating consequences for them," the report said.

As many as 75 percent of child bombers were girls, the UNICEF report said, adding that the youngsters had survived captivity and sexual violence only to be sent to their early graves. If they escape, many are shunned, even at camps for displaced people.

UNICEF cited the example of 17-year-old Khadija, who grew up in Cameroon and was kidnapped while visiting her mother in Nigeria and forced to "marry" a rebel fighter.

"Some women would beat me, they would chase me away (from the camp)...Everywhere I went, they would abuse me and call me a Boko Haram wife," the UNICEF report quoted Khadija as saying.

Last year, 151 suicide attacks, blamed on the Islamist Boko Haram network, were carried out by people of all ages in four countries, Nigeria, Cameroon, Chad and Niger.

The terror group sent bombers to mosques, marketplaces and other soft targets, and is believed to be turning captives into weapons.

#bringbackourgirls

Boko Haram were also responsible for the abduction of 276 girls from a school in the small northern Nigerian town of Chibok in April 2014, exactly two years ago on Tuesday.

UN human rights monitors criticized Nigeria for not doing enough to secure the youngsters' release. More than 200 are still missing.

"In the last two years, despite re-assurances from those at the highest level of the Nigerian Government, the parents have not seen any concrete progress in locating and liberating their daughters," the group of independent UN rights experts said.

An estimated 20,000 people have been killed since Boko Haram launched its campaign of violence in 2009, aiming to carve out a hardline Islamic state in northeast Nigeria.