A Myanmar military airstrike on a school last week killed at least 19 students, an ethnic militia said, as the war-torn nation's ruling junta steps up a campaign to retake territory ahead of a planned election in December.

Children were killed and injured at the boarding school in Kyauktaw township in Myanmar's restive Rakhine state, the U.N. children's agency, UNICEF, said in a statement.

It did not say how many were killed in the incident, but the Arakan Army, a militia battling the military in the western state, said at least 19 people between the ages of 15 and 21 had died.