The attack, beginning at the same time as an assault 250 miles eastwards in the city of Hassakah, has been seen as an attempt by Isil to stretch Kurdish forces to breaking point, diverting attention away from the militants’ Raqqa heartlands. A coalition of YPG and rebel fighters seized the strategically important border town of Tel Abyad from Isil in mid-June, cutting a key route through which foreign fighters and supplies have been ferried through Syria.