As the U.S. and Russian proxies have advanced from opposite sides of the river, which bisects Deir az-Zor province, the two sides accuses each other while tension escalates.
Russian airstrikes targeted the U.S.-backed Syrian Democratic Forces (SDF), which is predominantly led by the PKK's Syrian affiliate, the People's Protection Units (YPG), east of the Euphrates River in Syria's Deir az-Zor province, according to the Pentagon on Saturday. "Russian munitions impacted a location known to the Russians to contain Syrian Democratic Forces and coalition advisers," the Pentagon said.
Russia's military spokesman earlier denied targeting the SDF. "This is not possible. Why would we bomb them?" Igor Konashenkov, Russia's military spokesman, told AFP news agency at the Hmeimim base, Moscow's main outpost for its air operations in Syria.
The two offensives have often served as a dividing line between Russian and U.S. battles against Daesh in Syria. The attack was first reported by the SDF in a statement, which accused the Syrian regime - backed by the Russian Air Force - of trying to obstruct its fighters as both of the forces battle the Daesh in oil-rich Deir az-Zor province. Such attacks "waste energies that should be used against terrorism [...] and open the door to side conflicts," it said.
Meanwhile, Syrian regime troops seized a suburb of the city of Deir al-Zor in eastern Syria yesterday, tightening the noose around Islamic State militants, a military source said. Russia's RIA news agency cited an unnamed source as saying that the Syrian army cut Daesh's main supply line in the city on Sunday after taking control of the al-Jafra district.
The oil-rich Deir al-Zor province borders Iraq and is a strategic prize for both the U.S.-backed SDF and Russian-supported Syrian regime troops.
Backed by the U.S., the SDF started battling inside the historic old city of Raqqa, Daesh's de facto capital in Syria, in June, after months of fighting to encircle Raqqa with airstrikes and special forces from the U.S.-led coalition. The SDF has seized around 65 percent of Raqqa city, which lies directly west of Deir al-Zor province. As Daesh comes under pressure in Raqqa, many of its forces have fallen back on the towns and cities further east along the Euphrates River in Deir az-Zor province.
Deir az-Zor is southeast of Daesh's former base of operations in Raqqa city. Both cities lie in oil-rich areas on the Euphrates river. The terrorists have lost Iraq's second city, Mosul, and more than half of their de facto Syrian capital Raqqa. Deir az-Zor province is the last one in Syria still largely under terrorist control. U.S. support of the SDF, led by the YPG, and partnership in the operation has become a matter of dispute with Turkey, which says one terrorist group cannot be eradicated by another.