BEIRUT (AP) — U.S.-backed Kurdish-led fighters in northern Syria have launched a new offensive that aims to capture towns and villages east of the Islamic State -held northern city of Raqqa.

The new offensive by the Syria Democratic Forces was announced Saturday in a statement read by spokeswoman Cihan Sheikh Ehmed. She said it is the third phase of the Raqqa operation, which began last November.

The aim of the operation is to isolate Raqqa from the rest of IS-held territories before storming the city itself. The announcement came a day after aircraft from the U.S.-led coalition destroyed two bridges on the southern edge of Raqqa, the de facto capital of IS' self-declared caliphate.