Fighting has flared up between rebel brigades aligned with Ankara and a Kurdish militia in Aleppo governorate, a once sleepy front in the Syrian civil war that could be impacted by a Turkish drive to mend relations with President Bashar Al Assad.
At least one fighter from Tahrir Al Sham, an Al Qaeda offshoot that has channels with Turkey, has been killed in tit-for-tat attacks in the past 72 hours, with undetermined casualties from the SDF, a Kurdish-dominated militia, local sources said.
Tensions increased on the rebel-Kurdish militia front in Aleppo, which borders Turkey, after a car bomb at a roadblock near the rebel city of Azaz last week reportedly killed at least eight people. No one claimed responsibility, although many suspected the SDF.
A senior member of the Syrian opposition to Mr Assad told The National from Istanbul that half those dead were Turkish security personnel, although there was no announcement from Ankara.
Ensuing rebel attacks on the SDF constitute “Turkey's response to the Azaz car bomb”, the source said.
Turkey carved out a border zone in 2015 to check territorial gains by the Kurdish militias, who had managed to secure both US and Russian support, although Washington streamlined the militias under the SDF banner in 2015.
Failaq Al Sham, a Turkish-sponsored brigade linked to the Muslim Brotherhood, said it had foiled an SDF “infiltration attempt” on the Kabashin Axis on Sunday.
The axis is a military term for the front between the SDF enclave of Tal Rifat and the rebel-held area of Afrin, west of the provincial capital Aleppo city.
A “well-executed trap”, in which Failaq Al Sham used machine guns and artillery, caused “a number of deaths” among the SDF, Failaq Al Sham said.
Fighting also occurred overnight on Monday in Jibreen, near Azaz, but no casualties were reported, the sources said.
The Aleppo governorate is divided between Mr Assad's loyalists, the SDF, and rebel auxiliaries aligned with Turkey. Survival of the three sides has largely depended on the outside powers influencing the Syrian civil war: Iran, Russia, Turkey and the US.
Although the SDF was set up by Washington, Russian support enabled it to overrun rebel areas and establish a Kurdish-run enclave in Tal Rifat in 2016. Agreements between Moscow and Ankara ensured that hostilities involving the Tal Rifat Kurds remained at a relative minimum.
In the same year, the SDF helped Russian and regime forces, as well as pro-Iranian Shiite militias to capture the city of Aleppo. The SDF has safe passage through territory held by the regime to a larger zone it controls in eastern Syria, and which is also patrolled by US forces.
One opposition military source in Aleppo said Tahrir Al Sham and its allies “had little choice except to launch the operations” against the SDF, to maintain ties with Turkey.
This is despite positive Turkish moves in recent months responding to a Russian initiative to end hostilities between Damascus and Ankara.
On Monday, pressure from Turkey led to the reopening of a crossing in Aleppo, allowing goods to pass between rebel-held areas and territories under the authority of Damascus, according to several opposition members.
Crowds angry at the proposed rapprochement had overrun the rebel side of the crossing last month, forcing to close only days after it had opened.