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ISLAMABAD (AP) — Unexploded ordnance detonated Saturday in southern Afghanistan killing four children and injuring three others after the kids brought it inside their school, police and a doctor said.

The incident in Helmand province happened when the children discovered an unexploded shell and brought it inside their religious school and started playing with it, according a statement from the provincial police chief’s office.

The children were ages 7 to 14 and at least three others were injured, according to the police statement.

Afghanistan has suffered from decades of war and remains highly dangerous for children, who often collect scrap metal to sell to support their families. Many are killed or maimed when they come across unexploded ordinance.

Three of the children in Saturday’s explosion were killed immediately and a girl later died from her wounds at the hospital in Lashkar Gah, the provincial capital, according to a doctor there. The physician spoke on condition of anonymity because he was not allowed to address the media.