Activists say the U.S.-led coalition has carried out more than a dozen airstrikes in and around the Islamic State group's de-facto capital in northeastern Syria.

The air raids struck several areas overnight on the outskirts of the city of Raqqa along the Euphrates River. It was the heaviest round of coalition strikes on the city since Islamic State group militants captured a Jordanian pilot after his F-16 jet went down near Raqqa on Dec. 24.

The anti-Islamic State activist group called Raqqa is Silently Being Slaughtered reported on Friday at least 13 coalition strikes. The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees activist collective also confirmed the air raids.

There was no immediate word on casualties.