The Kurdish-led forces in Syria have said 38 ISIL fighters have been killed in a US-backed offensive against the group's final enclave after the area saw heavy bombardments overnight.

Three Syrian Democratic Forces (SDF) fighters were also killed in the battle, Mustafa Bali, the head of the SDF media office, said in a post on Twitter.

The members of the SDF moved towards a tent encampment in the village of Baghouz and at one point encircled a group of ISIL fighters, killing a number of them in an hour-long battle, Bali said. Al Jazeera's Hoda Abdel-Hamid said the fighting was the "heaviest yet" in the battle to retake Baghouz. "Coalition forces have carried out about 30 air strikes hitting defence positions but also weapon storage facilities," she said, speaking from the Turkish border town of Gaziantep.

After weeks of besieging Baghouz, the operation launched on Sunday night aimed at finally taking the last tiny patch of land held by ISIL, a pocket on the banks of the Euphrates River in eastern Syria near the border with Iraq.