Save the Children said it had spoken to displaced families who described “horrifying scenes” of murder, including mothers whose young sons were killed. In one case, the woman hid, helpless, with her three other children as her 12-year-old was murdered nearby.

“We tried to escape to the woods, but they took my eldest son and beheaded him,” the 28-year-old, who Save the Children called Elsa, is quoted as saying.

“We couldn’t do anything because we would be killed too.”

Another mother, a 29-year-old Save the Children calls Amelia, said her son was just 11 when he was killed by armed men.

Reuters could not immediately reach Mozambique police or government spokespeople for comment.

Mozambique’s northernmost province of Cabo Delgado has since 2017 been home to a festering insurgency, linked to Islamic State, that has escalated dramatically in the past year.

While beheadings have always been a hallmark of the attacks, throughout 2020 the insurgents began regularly engaging the military to capture and hold key towns. Brutality also continued, with mass killings including the murder of around 52 people at once in the village of Xitaxi in April.

Altogether almost 2,700 people on all sides have died in the violence, according to the Armed Conflict Location & Event Data Project (ACLED), a consultancy that tracks political violence. Almost 670,000 people have been displaced, Save the Children said.

The United States last week declared the Mozambique group a foreign terrorist organisation over its links to Islamic State, saying the group reportedly pledged allegiance to it as early as 2018. Islamic State claimed its first attack in Cabo Delgado in June 2019.

The U.S. embassy in Mozambique on Monday said U.S. special forces will train Mozambican marines for two months, with the country also providing medical and communications equipment, to help Mozambique combat the insurgency.

Amnesty International found earlier in March that war crimes were being committed by all sides in the conflict, with government forces also responsible for abuses against civilians – a charge the government has denied.

Chance Briggs, Save the Children’s country director in Mozambique, said reports of attacks on children “sicken us to our core”.

“The violence has to stop and displaced families need to be supported as they find their bearings and recover from trauma,” Briggs continued. (Reporting by Emma Rumney; Additional reporting for Manuel Mucari, William Maclean)