Airstrikes Hit Multiple Islamic State Targets in Syria Stronghold

US-led coalition forces said they carried out a series of 16 airstrikes on Saturday on the Islamic State in its Syrian stronghold of Raqa, in one of the biggest assaults on the extremists.

"The significant airstrikes tonight were executed to deny Daesh (IS) the ability to move military capabilities throughout Syria and into Iraq," spokesman Lieutenant Colonel Thomas Gilleran said in a coalition statement.

"This was one of the largest deliberate engagements we have conducted to date in Syria and it will have debilitating effects on Daesh's ability to move from Raqa."

Coalition forces "successfully engaged multiple targets" throughout Raqa -- the extremists' de facto capital -- the statement said, destroying IS structures and transit routes.

The strikes "have severely constricted terrorist freedom of movement," it added.

The announcement came after the self-proclaimed Islamic State group released a video showing teenage members executing 25 Syrian soldiers in an amphitheater in the ancient ruins of Palmyra.

The Syrian Observatory for Human Rights meanwhile reported heavy clashes in several parts of western Aleppo.