Warplanes pounded the Islamic State group's de facto Syrian capital Raqa on Tuesday, killing at least 23 people including 13 jihadists, a monitoring group said.
The British-based Syrian Observatory for Human Rights said that either regime or Russian warplanes are believed to have carried out the strikes.
"Thirteen members of the Islamic State group and 10 civilians were killed in at least 16 air raids on the group's positions and premises in several parts of Raqa city," Observatory chief Rami Abdel Rahman said.
He said the toll relied on information from only one hospital in the area because of security restrictions and that the number of dead could be higher.
IS seized Raqa in January 2014, expelling various rebel groups that had seized it from the regime the previous year.
Since then it has become the de facto Syrian capital of the territory controlled by the group, which it dubs an Islamic "caliphate".
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The town has been targeted by Syrian government air strikes and raids launched by Russia since its air campaign began in late September.
A US-led coalition fighting IS has also bombed the city in the past.
In Syria's second city Aleppo, at least 10 people were killed in air strikes on a southern neighbourhood currently under rebel control, the Observatory said.
It said all 10 were civilians and that the dead included three children, but was unable to determine if the raids were by Syrian or Russian aircraft.
Elsewhere, the Observatory said a Kurdish-Arab alliance had advanced against IS in the northeastern province of Hasakeh.
The Observatory said at least seven IS fighters had been killed in clashes with the Syrian Democratic Forces and air strikes by the US-led coalition on Tuesday.
The SDF said Saturday it had begun its first offensive since announcing the coalition last month against IS in Hasakeh province.