At least 32 Islamic State fighters were killed and 40 more wounded in Syria's Raqqa province on Sunday, in a series of air strikes believed to be carried out by a US-led coalition targeting the jihadists, a monitoring group said.
More than 15 explosions hit Islamic State positions in the countryside of Raqqa province and near its capital, Raqqa city, the Britain-based Syrian Observatory for Human Rights said. Raqqa is Islamic State's Syrian stronghold.
The coalition said it hit Raqqa and other areas of northern and eastern Syria on Sunday.
In central Syria, at least 45 air strikes, probably carried out by Russia, hit the city of Palmyra, which is also under Islamic State's control, the Observatory said. Injuries were reported, but no details on the casualty toll were available.
The United States and its allies have been bombing Islamic State in Iraq and Syria in an effort to drive the group from swathes of territory it controls in both countries.
Britain joined the effort this week after lawmakers approved bombing Islamic State targets in Syria. Hours after the vote, British bombers struck oilfields the government says are being used to fund attacks on the West. They made a second round of strikes on Friday.
Russia is waging a separate air campaign in Syria, which it launched on September 30 in support of its ally President Bashar al-Assad. Russia has said its air campaign targets Islamic State, but the West says most raids have hit other foreign-backed rebel groups.
