ISIS fighters marching in Raqqa, Syria.

At least 32 Islamic State of Iraq and Syria (ISIS) group fighters were killed on Sunday in apparent U.S.-led coalition air strikes on the group’s Syrian stronghold of Raqa province, a monitor said.

Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said that more than 40 ISIS jihadists were also wounded “in a series of around 15 strikes on ISIS bases by planes believed to be from the U.S.-led coalition”.

He said the wave of raids hit ISIS bases to the north, east and southeast of Raqa city, which is the group’s de facto Syrian headquarters.

Abdel Rahman said the casualty figures were collected from a single hospital and the final toll from the air strikes could rise.

The U.S.-led coalition has been carrying out strikes against IS in Syria since last September, expanding a campaign that began with raids in neighbouring Iraq.

ISIS controls large stretches of territory in the two countries, which it describes as an Islamic “caliphate”.

The U.S.-led coalition has expanded its operations in recent days, partly in response to the deadly attacks in Paris claimed by ISIS.

Britain voted on Wednesday to join the coalition’s strikes in Syria, after a heated debate in the country’s parliament and with the staunch backing of Prime Minister David Cameron.

And German lawmakers on Friday approved plans to join the military action against the group in Syria.

Raqa is frequently the target of air strikes by the U.S.-led coalition, as well as the Syrian air force and Russian warplanes that began an air campaign in Syria in late September.

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