BEIRUT (AP) — Syrian opposition activists say 15 civilians including children have been killed when a missile slammed into a government-held besieged neighborhood in the eastern city of Deir el-Zour.

The DeirEzzor 24 monitoring group said the missile hit near a school Thursday evening in the Qusour neighborhood. Among those killed were three children and three women, it said Friday, blaming the Islamic State group for the attack.

It said the attack destroyed the school and a nearby residential building.

The Britain-based Syrian Observatory for Human Rights also reported the incident, putting the number of civilians killed at 13.

Syrian troops broke a nearly three-year siege on parts of Deir el-Zour last month and are fighting to liberate from IS remaining parts of the city.