Missiles fired by Syrian regime forces killed nine civilians including five children in a school in north-western Syria on Wednesday, a war monitor said.
Part of the building in the town of Sarmeen had been turned into a shelter for the displaced, the Syrian Observatory for Human Rights said from Britain.
Fifteen people were wounded, Observatory head Rami Abdulrahman said.
The remains of a missile several metres long were found in a nearby olive grove.
In the latest round of violence in Syria's nearly nine-year war, regime forces have increased their deadly bombardment of the north-western opposition bastion of Idlib in recent weeks.
In December, the violence pushed about 284,000 people from their homes in the militant-run region of about 3 million people, the UN says.
The mass movement of people has led to public buildings such as mosques, garages, wedding halls and schools being turned into shelters, the UN humanitarian agency says.
Regime ally Russia announced a ceasefire for Idlib in late August. But sporadic clashes and shelling persisted through autumn before a sharp rise in violence in the past month, the Observatory said.
Syria's civil war has killed more than 370,000 people since it started in 2011 with the brutal repression of anti-government protests.
In total, 11,215 people including more than 1,000 children were killed during the war last year, although it was the least deadly year since the start of the conflict.