A series of U.S.-led coalition airstrikes targeting the Islamic State group's stronghold of Raqqa in eastern Syria has killed at least 10 militants and wounded many others.

The airstrikes were confirmed by the coalition, Raqqa-base activists and the Islamic State group.

In a statement issued early Sunday, the coalition said it had conducted 16 airstrikes throughout Raqqa, destroying vital IS-controlled structures and transit routes in Syria.

An IS-affiliated militant website confirmed the strikes on the center of the city. It said 10 people were killed and dozens wounded.

Activists reported hearing a series of loud explosions that shook Raqqa.

Raqqa is the de facto capital of the so-called Islamic caliphate declared a year ago by the Islamic State group in territories it controls in Iraq and Syria.