This year has seen an "alarming surge" in the use of children, in particular girls, to carry out violent attacks by terror group Boko Haram in the Lake Chad region, UNICEF has warned.

A report launched by the organisation this week, Silent Shame: Bringing out the voices of children caught in the Lake Chad crisis, shows that the number of children used in suicide attacks in the first quarter of this year has surged to 27 compared with nine over the same period last year. It says that takes to 117 the number of children used to carry out attacks in Nigeria, Chad, Niger and Cameroon since 2014. More than 80 per cent of those used in such attacks have been girls.

Marie-Pierre Poirier, UNICEF’s regional director for West and Central Africa, said the figure for the first three months of 2017 almost equals that of the entire of last year - 30 - in what she said is the "worst possible use of children in conflict".

“These children are victims, not perpetrators. Forcing or deceiving them into committing such horrific acts is reprehensible.”

UNICEF says the use of children to carry bombs has seen girls, boys and even infants being viewed with "increasing fear" at markets and checkpoints.

"The rise in these attacks is deeply troubling for both the civilian victims and for the children being forced to carry out the bombings," the report says. "Children have been intercepted at checkpoints and taken into military custody for questioning, raising concerns about this practice and the prolonged periods of custody."

The report said it is unclear whether some of the children are aware of what they are being asked to do. "That they are carrying explosives in a belt on their chests is incontrovertible, but it has been diffcult to ascertain if some of these children are being used to transport the devices to other locations and other active combatants or if they are being forced into a perverse death mission in exchange for promised redemption and martyrdom."

It said the upward trend in the use of children is a "defining feature" of the conflict in the region which has been going on for almost eight years.

UNICEF has said more needs to be done to protect children caught up in the conflict, including those who become associated with an armed group. They say children who have been taken into custody for their alleged or actual association with armed groups should be immediately released and referred to civilian authorities for reintegration support.

The report was released three years since the abducation of some 276 schoolgirls from their school in Chibok, Nigeria. More than 190 of the girls are still missing.