Rare clashes broke out yesterday between Syrian regime forces and a US-backed alliance in the east of the country, killing six alliance fighters, the Syrian Observatory for Human Rights monitor said.
State news agency SANA said the army seized control of four villages from the US-backed Syrian Democratic Forces in Deir Ezzor province, where the Kurdish-led alliance has been fighting the Islamic State jihadist group.
The SDF and Russian-backed Syrian government forces are conducting parallel but separate offensives against IS in the oil-rich province. But both sides have largely avoided running into each other and a deconfliction line exists to avoid such incidents.
The Kurdish-led alliance is present on the eastern side of the Euphrates River that cuts across Deir Ezzor province, while regime forces hold territory on the river's western bank, including the provincial capital of the same name.
Incidents between both sides have occurred in the past, but Observatory head Rami Abdel Rahman said it was the first time the regime had launched an operation to seize territory from the SDF.
In February, the US-led coalition backing the SDF carried out air strikes in Deir Ezzor province that killed at least 100 pro-regime fighters. Washington said the strikes were in retaliation for an attack on its own personnel and SDF forces.
In September last year, the SDF accused Russia of killing one of its fighters in strikes on a gas facility newly retaken from IS.
IS jihadists have lost most of the self-proclaimed "caliphate" they once controlled in large parts of Syria and neighbouring Iraq since 2014. Today, the jihadists hold less than four percent of Syria, the Observatory says.
This includes desert pockets in Deir Ezzor province and parts of southern Damascus where they are under attack by regime forces.