Jaish al-Islam had maintained control over the town since 2016 under a "reconciliation" agreement with regime forces, whereby they would not fire at each other.
But the new deal, SANA reported, "provides for the departure of around 1,000 terrorists from Jaish al-Islam to Jarabulus," a rebel-controlled northern town. Rebels had already begun handing over heavy weapons as part of the agreement, it said. Jaish al-Islam has not commented on the deal.
It comes three days after Jaish al-Islam evacuated the last opposition-held town in the onetime rebel bastion of Eastern Ghouta. Their departure paved the way for the Syrian army to declare its full control over Ghouta, after a ferocious two-month military assault on the enclave.
"This is why they're replacing the reconciliation deals with evacuation agreements," he told AFP.
Similar rebel departures were being negotiated for other nearby towns and for areas south of Damascus including Yalda, Beit Saham, and Babila, the Observatory said.
Meanwhile, government forces were preparing an assault on neighbourhoods in southern Damascus held by the Islamic State group.
The Observatory said that regime forces had fired dozens of shells and rockets onto the areas overnight and that IS had retaliated with shelling on Damascus that left one child dead.
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