At least 26 Syrian regime forces and members of their allied militias were killed on Tuesday in an ambush by the ISIS terrorist group in the Syrian Badiya, said the Syrian Observatory for Human Rights.
The attack took place at dawn against one of their posts in the Badiya, said the rights group.
The British-based monitor said 17 non-Syrians, among them Iranians, were killed in the attack.
The Badiya is a vast desert region stretching from central Syria to the eastern border with Iraq, where ISIS still holds small pockets.
Observatory chief Rami Abdel Rahman said the attack hit a small base east of Palmyra, the famed ancient city that ISIS has overrun twice in Syria's war.
"It began with a car bomb targeting regime forces that set off clashes that are still ongoing," he said.
A former resident from the eastern Homs countryside near Palmyra who is in touch with local people said the terrorists had come from hideouts in the vast stretch of desert they once controlled.
Five militants were also killed.
"ISIS fighters launched their attack from a pocket they control in the Badiya, and which was the destination for ISIS fighters evacuated from southern Damascus on Sunday and Monday," Abdel Rahman added.
Syria's regime on Monday seized a southern pocket of the capital from ISIS, announcing that the regime was back in full control of Damascus and its outskirts.
The Observatory, as well as a military source close to the regime, said the capture came after ISIS members were bussed out of the zone to desert territory.
