The US Central Command stated that pro-government forces had "initiated an unprovoked attack against well-established Syrian Democratic Forces headquarters" in the area, while coalition service members were "co-located with SDF partners during the attack 8 kilometers (5 mi) east of the agreed-upon Euphrates River de-confliction line".[20][21][22] The RussianMinistry of Defence's statement, released on 8 February 2018, referred to the incident at the village of Salihiyah (located south of the SDF-held town of Abu Hamam in the Abu Kamal District) and said that it was caused by reconnaissance actions of Syrian militias that had not been cleared with the Russian operations command; the statement stressed that there were no Russian service members in the "designated district of the Deir ez-Zor province of Syria".[23][24]
The number of pro-Syrian government troops–particularly the number of Russian mercenaries–has been the subject of debate.[19]: 49 Shortly after the fighting, the American officials estimated that around 100 Syrian troops had been killed in the fighting, with some reports of Russian mercenaries among the dead.[13] As unconfirmed accounts of casualties among Russian Wagner Group mercenaries in the strike emerged, the incident was billed by media as "the first deadly clash between citizens of Russia and the United States since the Cold War".[25]
Reporting by Der Spiegel and the official Russian position hold that U.S. troops repelling a Syrian attack "happened to kill 20–30 Russians", while the Syrian Observatory for Human Rights (SOHR) believed there were some Russian casualties caused by a nearby booby-trap unrelated to the assault. However, other news organizations and American official estimates ranged up to a "couple of hundred" Russians killed. The Ukrainian Security Service of Ukraine identified 65 Russians as killed through open-source intelligence, though this appraisal has the potential for forgery. A report published the University of Southern Denmark in 2019 which referred to claims made by Der Spiegel's report, official Russian and American statements, and other sources estimated "that 65–200 Russians (of which a few may have been Russian special operators assisting or leading the Wagnerites) died as a result of the fighting, some in the field, and some in hospital beds in Syria and Russia".[19]: 49–54