BEIRUT (AFP) - Syrian Kurdish forces on Monday cut a vital supply road linking the flashpoint border town of Tal Abyad to the Islamic State in Iraq and Syria (ISIS) group's bastion of Raqa, a Kurdish commander told AFP.

"The Kurdish People's Protection Units (YPG) have cut the route" leading south out of Tal Abyad, which lies on the Syrian-Turkish border, said Kurdish commander Hussein Khojer.

"Tal Abyad is completely surrounded," Mr Khojer told AFP, speaking by phone from near the town. "There is nowhere Daesh can escape to," he said, using the Arabic acronym for ISIS.

Mr Khojer said Kurdish fighters, backed by Syrian rebel groups, had advanced on the strategic town in a two-front offensive from east and west. "The YPG units from Kobane (in the west) and Jazira (in the east) met up south of Tal Abyad," he added.

Mr Sherfan Darwish, a spokesman for the Burkan al-Furat rebel group fighting alongside the YPG, said the anti-ISIS alliance had advanced to the "outer neighbourhoods" of the town's east and south.

"There are intense clashes there with Daesh," Mr Darwish told AFP, saying at least 19 ISIS militants were killed on Monday.

He confirmed that Kurdish forces and their rebel allies had cut the road south of Tal Abyad, adding that most of the border town's civilian residents had already fled the intensifying violence.

Mr Khojer said Kurdish forces were being backed by US-led coalition air raids.