On September 28, ISIS assault groups, supported by battle tanks and technicals armed with heavy guns, attacked government forces in few points at the Palmyra-Deir Ezzor highway, the key government supply line to Deir Ezzor city.
ISIS attacks took place at Ash-Shula, Bir-Ghabaghib and Sukhnah as well as at other points along the highway. Using the surprise effect, ISIS entered Ash-Shula and Bir-Ghabaghib cutting off the highway.
The ISIS-linked news agency Amaq claimed that in total 100 Syrian Arab Army (SAA) soldiers were killed. Amaq added that ISIS members killed a Russian soldier and captured 2 others. These claims were rejected by the Russian Defense Ministry.
ISIS had been able to concentrate enough forces for this move 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 Kurdish autonomy. This led to a large-scale political crisis in Iraq and a diplomatic crisis in the region that could led to a new round of the war in Iraq.
By September 29, the SAA and its allies re-grouped and 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. Even when government troops restore the control over the highway, they will not be able to recover the time that they had lost combating ISIS in the area.
Meanwhile, the US-backed Syrian Democratic Forces (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.
The SDF is actively exploiting the fact that ISIS is mainly focused on combating government forces in central Syria.