Syrian Kurdish-led forces said they had captured a town at the Turkish border from Islamic State on Monday, driving it away from the frontier in an advance backed by U.S.-led airstrikes that has thrust deep into the jihadis' Syria stronghold.

The capture of Tel Abyad by the Kurdish YPG and smaller Syrian rebel groups means the Syrian Kurds effectively control some 400 km (250 miles) of the Syrian-Turkish border that has been a conduit for foreign fighters joining Islamic State.

While the advance has brought the well-organized YPG deep into Islamic State's stronghold of Raqqa province, it has also concerned Turkey, which is worried the expansion of Kurdish sway risks inflaming separatist sentiment among its Kurdish minority.