Western-backed forces say they plan to crush the Islamic State terror group within two days after launching an operation to clear out the group's final stronghold.

The Syrian Democratic Forces, the Kurdish-led group that has been the US-led coalition’s main ally against Islamic State of Iraq and the Levant (Isil) in Syria, commenced their final assault on the village of Baghuz just after sunset on Friday night.

“After evacuation of thousands of civilians and our comrades who were held hostage in Baghouz, the operation to clear the last remaining pocket of Isil started at 18:00 this evening,” Mustafa Bali, a spokesman for the SDF said.

Mr Bali told The Daily Telegraph that said the operation is expected to last two days, but may take a week to complete as hardened jihadists fight back with heavy weapons and suicide car bombs.

Isil, which once ruled over eight million people in a proto-state covering large swathes of Syria and Iraq, now controls a patch of land about 700 metres across on the banks of the Euphrates river.