Armed groups in Mozambique are increasingly kidnapping children as a warfare tactic, putting victims at risk of sexual violence, early marriage and being used as fighters in the country’s worsening conflict, aid groups said on Wednesday.

At least 51 children have been abducted over the last year in violence that has killed thousands and displaced many more in a northern region torn by an Islamist insurgency, but aid workers say the true number of kidnappings could be much higher.

“Abducting a child constitutes one of the six grave violations against children in times of conflict, as defined by the United Nations,” said Chance Briggs, Mozambique country director for charity Save the Children.

“The experience of being abducted can have an immediate and lasting impact and consequences for boys and girls (including) death, sexual violence, exploitation and abuse,” Briggs told the Thomson Reuters Foundation in emailed comments.

Read more: Reuters