Commanders of a U.S.-backed Syrian force fighting the Islamic State group in Syria say intense fighting is taking place as fighters advance toward the last piece of territory held by the extremists.

Airstrikes by the U.S.-led coalition shook the ground on Sunday, and smoke was still billowing from a suspected weapons depot belonging to the militants that was struck a day earlier.

The Kurdish-led fighters, known as the Syrian Democratic Forces, resumed an offensive against IS on Friday night, after a two-week pause to allow for the evacuation of civilians from the area.

The capture of the last pocket still held by IS militants in Baghouz village would mark the end of a devastating four-year campaign to end the extremist group's hold on territory in Syria and Iraq.