Friday's bombardment ended two days of relative calm on the front line in the village of Baghouz near the Iraqi border.

The Kurdish-led Syrian Democratic Forces had paused its advance while it combed a makeshift jihadist encampment it overran on Tuesday.

An SDF official who asked not to be named said that warplanes of the US-led coalition resumed airstrikes on suspected jihadist positions in the early hours of the morning.

Top SDF commander Jia Furat said his forces were engaging with the jihadists on several fronts while the coalition warplanes provided air support.

The US-led coalition said the "operation to complete the liberation of Baghouz is ongoing".

"It remains a hard fight, and Daesh is showing that they intend to keep fighting for as long as possible," it said using an Arabic acronym for IS.

The SDF launched an assault against the jihadists' last redoubt in the village of Baghouz on February 9.

On Tuesday, they cornered diehard fighters into a few acres of farmland by the Euphrates River, after forcing them out of the encampment where they had been hold up.

The six-month-old operation to wipe out the last vestige of IS's once-sprawling proto-state is close to reaching its inevitable outcome.

But the SDF said on Thursday that a declaration of victory would be made only after mopping up operations had been completed.

IS declared a "caliphate" in June 2014 after seizing a vast swathe of territory larger than Britain straddling Iraq and Syria.

The loss of the Baghouz enclave would signal the final demise of the "caliphate" in Syria, after its defeat in Iraq in 2017.

But IS has already begun its transformation into a guerilla organisation, and still carries out deadly hit-and-run attacks from desert or mountain hideouts.

The war in Syria has killed more than 370,000 people and displaced millions since it erupted following the repression of anti-government protests in 2011.