U.S.-backed Syrian Democratic Forces (SDF) fire on Islamic State militant positions in Baghouz Image Credit: AP

Baghouz - Besieged by U.S.-backed forces in their last foothold in eastern Syria, Islamic State militants are calling on supporters across the world to stage attacks in their defense, according to a newly released audio recording.

The recording, purportedly from Daesh, came as the Kurdish-led Syrian Democratic Forces announced that offensive against Daesh final enclave in eastern Syria is basically over but requires a little more time to be completed on the ground.

"The operation is over, or as good as over, but requires a little more time to be completed practically," Kino Gabriel said in an interview to Al Hadath TV on Tuesday.

The brief, minute-and-a half recording, released by Daesh supporters on social media and reported by the SITE Intelligence Group late on Monday said that men, women and children in Baghouz are being subjected to a "holocaust by the Crusaders," which is militant jargon for the U.S.-led coalition against IS.

In the audio, an unidentified Daesh militant calls on Muslim "brothers, in Europe and in the whole world" to "rise against the Crusaders and ... take revenge for your religion." As the man speaks, cracks of gunfire can be heard in the background, apparently meant to suggest that he is in Baghouz.

"Crusaders warplanes" and "Kurdish atheists" are attacking his people, the man says. The recording's authenticity couldn't be independently verified.

The U.S.-backed forces resumed their offensive against Daesh on Sunday night, after thousands of civilians and hundreds of fighters left the last sliver held by the extremists. Since then, 38 militants and three SDF fighters have been killed, according to SDF spokesman Mustafa Bali.

Argish Al Deiri, an SDF commander in Baghouz who identified himself by his nom de guerre told The Associated Press on Tuesday that his men advanced overnight and secured some positions on the edge of a tent settlement where Daesh militants are making their last stand.

"We entered the camp, then stopped," he said. "There was resistance, and we withdrew. The planes struck the ammunition depot," setting off explosions that halted the push.

He said IS militants were fighting back with heavy weapons, rifles and sniper fire, forcing SDF fighters to slow their advance rather than advancing quickly so that "you don't lose your men."

He said he hoped the Daesh fighters will surrender in the coming "few days."

The capture of Baghouz would be a milestone in the devastating four-year campaign to defeat Daesh's so-called "caliphate," which once covered a vast territory straddling both Syria and Iraq.