That this incident was inadvertent on the part of the US is very plausible. In Deir ez-Zor Syrian soldiers have been entrenched in that city, with their base in its military airport, fighting off a two-year ISIS siege. The US coalition has also been bombing every ISIS-related target in that province they can find, from the marauding militants themselves to oil installations they have used to finance their savage conquests. And there is the fact that the US hasn’t been coordinating in any way with the Syrian regime. Something which was bound to be a problem sooner or later.
In Syria the US has been focused solely on bombing ISIS and, at times, the Islamist group formerly known as Jabhat al-Nusra (now Jabhat Fateh al-Sham). When The US first began bombing ISIS in northeastern Syria back in September 2014, they have refused to coordinate operations with the Syrian regime. As a precaution, the US fighter jets carried HARM anti-radiation missiles, in case Syrian air defenses would suddenly target them.
While Washington refused to coordinate with Damascus, US Secretary of State John Kerry did get Iraqi Foreign Minister Ibrahim al-Jaafari to give the Syrian regime a heads up about the US airstrikes against ISIS bases inside Syrian territory, assuring Damascus that their forces wouldn’t be targeted. Also, the fact that Syrian forces were mostly out of northeastern Syria — except for their footholds in Deir ez-Zor and the Kurdish-majority cities of al-Hasakah and al-Qamishli — when the US began their air campaign against ISIS, lessened the chance of any direct clash.
With the Russian military intervention in Syria in September 2015 the situation was different. The US, as well as Israel and Turkey, immediately established a communications mechanism with Moscow to ensure there would be no aerial clashes in Syria’s ridiculously congested airspace. Later, when the US deployed special forces to advise their Kurdish allies in the region, they also told the Russians the general areas where those forces are operating.
In August, Syrian bombers launched their first ever airstrikes against Kurdish forces in al-Hasakah after Kurdish and regime forces in that city began clashing. US special forces advisors nearby felt the shudder of the bombs impacting. The US responded by scrambling two F-22 Raptor stealth fighters, which flew to the area to warn off the Syrian planes. The following day the F-22’s came within a mile of Syrian Su-24 bombers in the same area. (Paul Sonne and Raja Abdulrahim, “Pentagon Warns Assad Regime to Avoid Action Near U.S. and Allied Forces“, The Wall Street Journal, 19.08.2016).
Following that incident, US Press Secretary Peter Cook told reporters that the US did contact the Russians through their communications mechanism “to have them communicate to the Syrian regime our concerns about what happened and the fact that it shouldn’t happen again. We will continue to use that as a resource given the Russian relationship with the Syrians. But we are also prepared to speak, engage directly, communicate directly [with the Syrians] if needed, in order to avoid these kinds of situations in the first place.”Yet a month after that dangerous incident the US has made this fatal mistake in Deir ez-Zor. To add insult to injury these airstrikes enabled ISIS to temporarily advance on regime positions in that contested city. Only subsequent supporting Russian airstrikes, which killed at least 20 of the militants, enabled the Syrian military to recapture that territory and prevent ISIS from overrunning any more of their positions.
Incidentally, it shouldn’t be forgotten that the Russians were involved in a not too dissimilar incident in Aleppo back in October 2015. Back then Russian aircraft bombarded rebel positions which were quickly overrun by ISIS in the militant groups most significant advance in the Aleppo province in two years.
Following this latest incident the US really needs to establish some form of a direct communications mechanism with Damascus, which would not violate Washington’s, understandable, aversion to any form of coordination with Syrian President Bashar al-Assad’s murderous regime. This should be done in clear recognition of the fact that nobody benefits in the long-term from any ISIS advances in that area, or for that matter in any area. Something that was the predictable, and tragic, result of this mistake in Deir ez-Zor which was not brought about by miscommunication, but by the complete lack of any communication.
The Syrian military declared Monday, two days after the incident, that the seven-day partial cease-fire in Syria was over. The US disputed the Syrian military’s declaration, suggesting that it would not consider the cease-fire over unless that was announced by Russia:
While we have seen comments attributed to the Syrian military, our arrangement is with Russia, which is responsible for the Syrian regime’s compliance, so we expect Russia to clarify their position. — John Kirby, Spokesperson for the United States Department of State, cited in Anne Barnard and Michael R. Gordon, “Syrian Military Declares Cease-Fire Over, but U.S. Says Talks With Russia Continue“, The New York Times, 19.09.2016.