The U.S.-backed New Syrian Army said it was forced to withdraw its forces to its base at Tanf near the Jordanian border after launching what appears to have been a poorly conceived offensive aimed at capturing the strategically important eastern Syrian town of Abu Kamal on the Syrian-Iraqi border.

Islamic State claims published by its Amaq news agency that its fighters had killed 40 members of the group and captured 15 could not be independently confirmed and appeared to be exaggerated. Islamic State social media accounts posted photographs and videos showing brutalized bodies, the beheading of one fighter and small quantities of captured, U.S.- supplied weaponry.

The New Syrian Army said in a statement only that it lost “several men” before the group “successfully departed” to Tanf, more than 150 miles away in remote desert terrain near the Jordanian and Iraqi borders…

The battle was a setback, they said, for a small group that was depleted further by an Islamic State suicide bomber in May and by a Russian airstrike in June. The group was formed last year with only about 100 men, and its ranks had dwindled significantly by the time the offensive was launched, according to commanders.