Kurdish forces and allied Arab fighters seized most of a key military airport and a nearby town in northern Syria from rival anti-regime factions, a monitoring group said.
The Kurdish People's Protection Units (YPG) and its Arab backers expelled Syrian rebel fighters from the town of Menagh and overran "more than half" of the nearby air base, north of Syria's second city Aleppo, the Syrian Observatory for Human Rights said.
The advance comes after days of fierce clashes that saw YPG forces advance east from the Kurdish stronghold of Afrin and take over a series of villages before reaching Menagh.
Clashes were ongoing inside the airport, where rebels were trying to maintain a grip on the last military air base they hold in Aleppo province, Observatory head Rami Abdel Rahman said.
There have been reports that the Kurdish fighters were aided by Russian bombing in the area, as Moscow's war planes look to support a regime advance against the rebels.
Regime forces lost Menagh airport to the rebels in August 2013.
Rebel groups are facing a twin advance by both Kurdish forces coming from the west and regime troops - backed by heavy Russian bombing - moving forward from northern Aleppo.
The Islamic State group are also attempting to take territory from the rebels in Aleppo province.
This has led the opposition to accuse the Kurds of a land grab and collaborating with the Syrian regime and Russia. The regime have also been accused of working with IS during the most recent landgrab.
More than 500 people have been killed since the regime began its Aleppo assault on 1 February, the Observatory said Wednesday.