ISIS still controls territory along the Turkish border with secondary roads to the frontier but these are more dangerous and difficult to access. (File Photo)
A US-backed Arab-Kurdish alliance on Friday severed the ISIS's main supply route to Turkey after encircling a key ISIS-held town in northern Syria, a monitor said.
"The Syrian Democratic Forces (SDF) cut off the last road from Manbij to the Turkish border on Friday morning," the Syrian Observatory for Human Rights said.
ISIS still controls territory along the Turkish border with secondary roads to the frontier but these are more dangerous and difficult to access, Observatory head Rami Abdel Rahman said.
This week the SDF, backed by air strikes by a US-led coalition, cut the road north out of Manbij to the ISIS-held border town of Jarabulus, which the terrorists had used as a transit point for fighters, money and weapons.
The SDF also blocked the road south out of Manbij heading to ISIS's de facto capital of Raqa.
"For the ISIS to reach the Turkish border from Raqa, they now have to take a route that is more dangerous because of regime troops nearby and Russian air strikes," Abdel Rahman said.
Russia launched air strikes in support of President Bashar al-Assad's regime in Syria in September.