The IS militant group launched a counter-attack against fighters trying to capture the Syrian city of Manbij on Monday, inflicting heavy casualties on the U.S.-backed forces.
The Syrian Observatory for Human Rights said the IS militants won back three villages south of the besieged city in a surprise assault against fighters from the U.S.-backed Syria Democratic Forces. At least 28 SDF fighters were killed.
Two years after IS proclaimed its caliphate to rule over all Muslims from swathes of territory in Iraq and Syria, its many foes are advancing on a number of fronts in both countries. Their aim is to close in on its two capitals, Raqqa in Syria and Mosul in Iraq.
The SDF were poised to enter Manbij nearly three weeks after the launch of a major assault to regain the city backed by U.S. air power and American Special Forces, to seal off the last stretch of the Syrian-Turkish frontier.
The alliance, formed last year by recruiting Arabs to join forces with a powerful Kurdish militia, fought to nearly 1.24 miles from the city centre from the western side on Saturday before retreating.
U.S-led coalition jets hit militants taking cover near a large wheat silo complex on the southern edge of the city that has been encircled by SDF forces.
An SDF spokesman said forces succeeded in repulsing the militant attack and remained positioned on the outskirts of the city, most of whose residents remain trapped inside due to mines planted by the militants, who have dug in to defend it.
IS militants were also able to roll back the Syrian army, which had reached as close as 6.2 miles south of the strategic town of Tabqa, an IS-held city on the Euphrates River, in Raqqa province.