Deir Ezzor, a Syrian city on the Euphrates River, has been a key base for ISIS since the group first captured a majority of the city back in 2014.
Pro-Assad regime forces, backed by Russian airstrikes, have recently made gains there and linked up with a group of beleaguered regime soldiers that were besieged there for nearly three years, according to Syria's official state-owned news agency.
In support of this push, two Russian submarines launched a barrage of cruise missiles Thursday targeting ISIS positions in Deir Ezzor, according to a statement issued by the Russian Ministry of Defense.
But the US-backed Syrian Democratic Forces recently announced their own push toward the city, "Operation Jazeera Storm," and a group of SDF fighters have made rapid gains, capturing some 300 square kilometers from ISIS along the Khabur River, which intersects with the Euphrates River just south of the city.
And the US-led coalition carried out its own airstrikes in Deir Ezzor, Wednesday, targeting ISIS fighters and vehicles.
The two simultaneous offensives in the direction of the ISIS-held city raised the prospect of a clash over who would be able to claim the Deir Ezzor prize. But a spokesman for the US-led coalition told reporters Thursday that the SDF would not enter the city, seemingly ensuring that the Russian-backed pro-regime troops would be the ones to capture it.
"The plan right now is not to go into the city," US Army Col. Ryan Dillon told reporters at the Pentagon via a teleconference from Baghdad.
The city sits on the northern end of the Middle Euphrates River Valley, an area where US officials believe ISIS has relocated much of it leadership and has thousands of its fighters.
"The last stand of ISIS will be in the Middle Euphrates River Valley," the then-commander of the coalition, Lt. Gen. Stuart Townsend, told reporters last month.
And many of the US-led coalition's local allies hail from the area and are eager to return home, something made more complicated by regime gains in the area.
"Arab SDF fighters native to the area are reuniting with friends and family they have been separated from for years due to ISIS terrorist control of the villages they called home," Dillon said Thursday.
Many of the US-backed fighters being trained at the joint garrison in At Tanf, Syria also come from this area and US officials have told CNN that the Assad regime has tried to woo these fighters away from their alliance with the US with promises of joining the regime's push in the area.
But while Dillon acknowledged that the US backed fighters would not go into the city, he said there were plenty of other ISIS targets further down the river.
"The plan is not to go into Deir Ezzor city but there is, you know, plenty of ISIS fighters and resources and leaders that continue to have holdouts throughout the Middle Euphrates River Valley," he said.
The regime and SDF advances are bringing the two forces into increasingly close proximity along the Euphrates, with Dillon saying that "increased" de-confliction was needed between Russia and the coalition as a result of the two sides being so close to one another.
"The convergence of military forces in this area calls for increased awareness and de-confliction," Dillon said.
De-confliction efforts were ramped up following a series of clashes several months ago between US-backed forces and forces allied to the regime which resulted in US warplanes downing two drones and a Syrian jet. And coalition officials have cited those efforts as the reason for the absence of any such clashes in recent weeks.
But with Russian and coalition military officers already using the communications hotline that allows the two sides to de-conflict their respective forces on a daily basis, it is difficult to imagine how such efforts can be increased without venturing into more active coordination.