PHOTO: Fighters of the Kurdish militia YPG in northern Syria

Kurdish militia clashed with rebels in northern Syria on Thursday, in some of the most serious fighting between the two sides during the country’s 56-month conflict.

The Kurdish force YPG, reportedly supported by the former rebel commander Jamal Maarouf, attacked rebel factions in northern Aleppo Province, according to pro-rebel activists and journalists.

Maarouf’s Syrian Revolutionary Front was supported with US money and weapons, and the commander was promoted by Washington as its preferred rebel leader in early 2014. However, the SRF fell out with other rebel groups over claims that Maarouf and his fighters were involved in crime, corruption, and war profiteering. In late 2014, the SRF was forced out of Syria after battles with Jabhat al-Nusra.

Pro-rebel outlets also claimed that the Kurds were backed by Russian airstrikes as they advanced towards the village of Malkiya. The area is close to the Bab al-Salama border crossing with Turkey, which has been under Russia aerial attack since Wednesday.

Rebels claimed that they repelled the attack, inflicting “heavy casualties” on the YPG.

In Aleppo city, the YPG — based in the Sheikh Maqsoud district — reportedly fired mortars on the only supply road into rebel-held sections.

The Kurdish militia and rebels have periodically fought over the past year, as rebels advanced in much of northwest Syria and Kurds consolidated their control of territory in the northeast along the Turkish border. Turkey has proposed a “safe zone”, a 98-km (61-mile) strip along the border, which nominally separates the Kurdish forces from rebels — the would rebels hold the area in Aleppo Province west of the Euphrates River, while Kurds would stay to the east.

However, one of the three Kurdish cantons in Syria, Afrin, is far to the west of the Euphrates in a northwestern Syrian pocket bordering Turkey, close to rebel-held towns such as Azaz and Atmeh. This summer, there was fighting between Afrin and Azaz and claims of YPG attacks on trucks on the supply road into Aleppo city.

See Syria Daily, August 30: Kurds and Rebels Clash Near Proposed “Safe Zone” in North

The head of the rebel operations room in Mare’ in northern Aleppo Province said it would intervene if the Kurds continued their attacks. He insisted there were no Islamic State forces in the area of the fighting, and that there were no elements from Jabhat al-Nusra in the rebel operations room.

He asserted, “As for the Kurds, we are brothers in religion and in our country.”