Syrian rebels are closing in on a town near the Turkish border held by Islamic State (IS) after seizing numerous villages from the group in the area, rebels and the Syrian Observatory for Human Rights say.
The rebels involved in the offensive include factions fighting under the banner of the Free Syrian Army that have been supplied with weapons via Turkey. They are advancing towards the IS-held town of al-Rai.
A sustained rebel advance near the Turkish border would erode IS's last foothold in an area identified by the US as a priority in the fight against the group.
Rebels who have previously struggled to make sustained gains against IS in the area have mobilised 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.
"The battles are continuing ... we have been able to liberate several villages very quickly from the Daesh gangs and God willing will cleanse northern Aleppo," said Abu Yasser, a commander with Failaq al Sham group, speaking to Reuters.
The Observatory said the rebel groups had seized at least 16 villages in an area held by IS for nearly two years.
IS's foothold at the Turkish border was significantly reduced last year by US-allied Kurdish fighters of the YPG, which gained territory from the group further east.
The YPG and rebels are however locked in their own conflict, notably near the city of Aleppo. Turkey, a major sponsor of groups fighting to topple Syrian President Bashar al-Assad, has been alarmed by YPG gains near the frontier with Syria.