Eight Syria Civil Defence workers died on Saturday when an air strike hit their office in northern Hama province, the rescue service said on its Twitter page.
Also known as the White Helmets, the civil defense rescue service operates in opposition-held parts of Syria.
The civil defense center was in Kafr Zeita, a town in rebel-held northern Hama province, which came under intense aerial bombardment on Saturday, the Syrian Observatory for Human Rights war monitor said.
Backed by Russian air strikes and Iranian-backed militias, the Syrian army is waging an offensive against rebel areas north of government-held Hama city, reversing insurgent gains made last month.
(Reporting by Lisa Barrington; Editing by Robin Pomeroy)