The monitor said factions fighting under the banner of the Free Syrian Army, some of whom are supplied with arms by Turkey and other foreign backers, had captured most of the previously IS-held town of al-Rai in northern Aleppo province.
A sustained rebel advance near the Turkish border this week that allowed them to capture a string of villages erodes Islamic State’s last foothold in an area identified by the United States as a priority in the fight against IS.
Rebels who have previously struggled to make gains against IS in the area and had been in recent weeks fending off advances by Kurdish-led fighters had mobilized several thousand fighters for the attack, rebel sources said.
An alliance of rebel groups formed for the offensive includes the Turkish-backed Sultan Murad and Failaq al Sham groups.
