On September 28, ISIS assault groups attacked government forces in few points at the Palmyra-Deir Ezzor highway, the key government supply line to Deir Ezzor city. ISIS used battle tanks, technicals with heavy guns and suicide bombers to break the Syrian Arab Army (SAA) defense.
The main ISIS attacks took place at Ash-Shula, Bir-Ghabaghib and Sukhnah. Following a series of clashes, ISIS entered Ash-Shula and Bir-Ghabaghib pushing the Syrian military to close the highway.
The ISIS-linked news agency Amaq claimed that in total 100 Syrian soldiers were killed. Separately, Amaq released claims that ISIS members killed a Russian soldier and captured 2 others. The Russian Defense Ministry denied these reports.
ISIS had been able to concentrate enough forces for this large advance thanks to the ongoing Arab-Kurdish tensions in Iraq that resulted in halting of Iraqi anti-ISIS operations near the border with Syria.
On September 25, the Iraqi Kurdistan Region Government held an independence referendum in the area controlled by its forces, including multiple areas that have never formally been a part of the Kurdistan Region. This led to a large-scale political crisis that could led to a new round of the war in Iraq.
On September 29, the SAA and its allies started a counter-attack in an attempt to regain points that they had lost at the highway. A fighting continued in Ash-Shula and Bir-Ghabaghib. The fighting is now ongoing in these areas.
Separately, ISIS conducted an attack on government forces near T3 Pumping Station east of Palmyra. The attack was repelled.
The US-backed Syrian Democratic Forces (SDF) are actively exploiting the fact that ISIS is mainly focused on combating government forces in central Syria.
On September 28, the SDF officially announced that it has seized al-Suwar town northwest of Deir Ezzor and started another operation in order to reach and to capture Markada town in southern Hasakah.
On September 29, Deputy Foreign Minister Oleg Syromolotov announced that Russia will not allow the United States as well as any other foreign power to limit an area of operations of the SAA in Deir Ezzor province. This could be described as a sign that government forces will continue its operation on the eastern bank of the Euphrates.
— Минобороны России (@mod_russia) 29 September 2017
Clashes in Deir Ezzor area: