They said a woman and a child were among those killed when several mortar rounds hit the hospital in the city of Atareb which was taken out of service.
Turkey's defense ministry earlier said on Sunday five people were killed and 10 injured in an artillery attack by Damascus-backed forces on a hospital in the northwest Syria, [S8N2JI00X] where they have a military presence.
Videos received by Reuters from two witnesses showed a ward damaged and civil defense rescuers carrying blood-stained patients outside. Reuters could not verify their authenticity.
Fighting between Syrian army forces and rebels has subsided since a deal a year ago ended a Russian-led bombing campaign that had displaced over a million people in the region which borders Turkey after months of fighting that killed several thousand civilians.