Heavy US-led ISIS raids in Raqa kill dozens

A US-led coalition has carried out some of its heaviest air strikes yet on the Islamic State group's de facto Syrian capital, killing more than 30 people, including six civilians.

The strikes on Saturday night and yesterday morning also damaged infrastructure in Raqa city, the group's bastion in northern Syria.

Elsewhere, regime forces backed by Lebanon's Hezbollah advanced on the last rebel-held town in the Qalamun region by the Lebanese border.

And fighting continued between government troops and two rebel coalitions seeking to capture territory from the regime in northern Aleppo city.

In Raqa, the Syrian Observatory for Human Rights said at least 30 people had been killed in US-led coalition strikes late Saturday and early yesterday.

The dead included six civilians, among them a child, but the rest were ISIS fighters, the Britain-based monitor said.

The US-led coalition said the strikes were some of its heaviest since it began carrying out raids against ISIS in Syria last September.

"The significant air strikes tonight were executed to deny Daesh (ISIS) 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 statement said, destroying ISIS structures and transit routes.

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

The raids came after ISIS released a video Saturday showing the execution of 25 Syrian soldiers in the ancient amphitheatre in the city of Palmyra.

The executions had been reported earlier, in the days after ISIS seized the town from government forces on May 21, but the video was the first evidence of the killings.