A Syrian rebel group which is part of a new U.S.-backed alliance that also includes the Kurdish YPG militia announced on Thursday plans for an imminent offensive against Islamic State militants in Raqqa province, the jihadists’ stronghold in Syria.

U.S. Defence Secretary Ashton Carter said earlier this week the U.S.-led coalition would support local forces as they put pressure on Islamic State in Raqqa and in neighboring Iraq.

Washington has announced a shake-up of its support to the rebels battling the forces of Syrian President Bashar al-Assad, ending a program to train fighters outside Syria and instead providing weapons to groups under U.S.-vetted commanders. It has already dropped ammunition to rebels in the north, but has not specified which groups the aid was bound for.