Yesterday’s US downing of a Syrian Su-22 bomber in Syria has provoked a major reaction from the Russian Defense Ministry, which warned today that it views the incident as a “massive violation of international law” on the part of the Americans, and will begin treating all US and US-led coalition jets west of the Euphrates River as hostile targets.
That would mean US warplanes can still operate in the territory of the Kurdish YPG, which except for the city of Manbij ends at the Euphrates River. It likely also leaves the US free to attack the ISIS capital of Raqqa, which is on the river, as well as much of the rest of ISIS territory in Syria.
Russia isn’t necessarily saying they’ll shoot down US planes if they stray across the river, but rather that they’ll track them as potential targets with their advanced surface-to-air missile systems deployed in Syria, which would allow them to open fire on the planes if they start attacking pro-Syrian forces again.
By far this would have the biggest impact on the rebel base at al-Tanf, which unsurprisingly is near where a lot of the recent problems with US warplanes attacking anti-ISIS forces seem to be happening. Tanf is well on the “wrong side” of the Euphrates, and Russia likely wants to send the message that the Tanf base, which has some US troops deployed within, does not grant the US carte blanche to attack all pro-government forces within the vicinity, especially since those forces have by and large been fighting ISIS and al-Qaeda.
It remains to be seen if the US will view this as a serious threat, or simply a bluff that they’re going to ignore. Since the US warplanes aren’t attacking Syrian forces daily, they may believe a few uneventful forays across the Euphrates prove that Russia’s warning isn’t sincere, risking catastrophe when, inevitably the US decides to go back to attacking Syrian forces.