Islamic State group jihadists killed nine Syrian students when they shelled a school in the eastern city of Deir Ezzor on Tuesday, state news agency SANA reported.
The Syrian Observatory for Human Rights said nine girls were killed and another 20 wounded, mostly students from the regime-held district of Hrabesh.
"The toll is likely to worsen as some of the injured are in serious condition," the Observatory's Rami Abdel Rahman told AFP.
The Islamic State group has controlled nearly all of oil-rich Deir Ezzor province since 2013, but half of the regional capital remains in the government's hands.
In recent weeks, the US-led coalition and Russia's military have targeted IS jihadists in the province with air strikes.