In the operation's early weeks, Jarabulus and Al-Rai became the first two major settlements to be captured from the IS.

The Syrian rebels, supported by Turkish planes and tanks, are two and a half kilometres (1.5 miles) from Dabiq, according to the British-based Syrian Observatory for Human Rights.

"Two hours ago, the rebels started their attack to control Dabiq. The rebels came from Al-Rai," it said.

Dabiq holds symbolic importance for Isil because of a Sunni prophecy that states it will be the site of an end-of-times battle between Christian forces and Muslims.

The town itself has negligible military value compared with the strategic Isil-controlled cities of Raqqa in Syria and Mosul in Iraq.