Town now target of intensive air strikes by both government and Russian aircraft
Islamic State (IS) group militants succeeded on Sunday in expelling Syrian government forces from the eastern town of Mayadeen, days after they entered the key remaining militant stronghold, a monitor said.
Backed by Russian air power, Syrian forces had managed to fight their way into western Mayadeen on Friday.
"Counter-offensives by IS managed to force the regime fighters away from the western outskirts of Mayadeen," the Britain-based Syrian Observatory for Human Rights said.
Observatory chief Rami Abdel Rahman said the Syrian forces were now 6km from the town, which was being targeted by "intensive air strikes carried out by both regime and Russian aircraft".
IS has controlled Mayadeen in Syria's eastern province of Deir Ezzor since 2014.
The town is on the western bank of the Euphrates River, between provincial capital Deir Ezzor, where the militants still hold several districts and the border with Iraq.
Many of the IS militants who fled an offensive by US-backed forces against the group's de facto Syrian capital Raqqa have decamped to the towns of Mayadeen and Albu Kamal in the Euphrates Valley.
The militants are being pressed by twin offensives in eastern Syria: by Russia-backed government forces and by the US-supported Arab-Kurd alliance, the Syrian Democratic Forces.