The chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford, told reporters at the Pentagon that negotiations with Moscow were underway and were aimed at allowing US and Russian forces to operate in proximity to one another.
"We had a proposal that we're working on with the Russians right now," Dunford said. "I won't share the details, but my sense is that the Russians are as enthusiastic as we are to de-conflict operations and ensure that we can continue to take the campaign to ISIS and ensure the safety of our personnel,"
Dunford said that the talks are focused in part on Deir ez-Zor, a Syrian city along the Euphrates River where ISIS fighters and Russian-backed regime forces are located. US officials have increasingly seen ISIS leadership leave Raqqa for Deir ez-Zor as the US-backed Syrian Democratic Forces begin closing in on Raqqa.
The latest effort will be in addition to the pre-existing hotline aimed at ensuring that US-led coalition and Russian forces avoid any accidental encounters in the air or on the ground in Syria.
The US military is prohibited by law from coordinating directly with the Russian military, but given the increased pace and scale of military operations in Syria, the US and Russia have sought ways to ensure that their respective personnel are not targeted by mistake, setting up a series of "de-confliction zones" that would delineate exclusive areas of operation for the coalition and the Russian forces.
The announcement comes just days after coalition warplanes bombed pro-regime forces near At Tanf, Syria, striking a convoy
that had entered one such "de-confliction zone" and was approaching a base used by US and coalition advisers.
Secretary of Defense James Mattis said that it appeared the Russians had attempted to get the militia convoy to turn around, but was unable to do so.
"We believe they moved into that zone against the advice of the Russians," Mattis said, adding that while he could not confirm the Russian effort, "it looks like the Russians tried to dissuade them."
Mattis called the fighters that were struck "Iranian directed forces," and a US defense official said they had likely been told to venture into the area by Iranian advisers.
Dunford and Mattis made a concerted effort to tout the changes made as part of the newly developed counter-ISIS strategy directed by President Donald Trump, citing the delegation of authority to commanders and a decision to surround ISIS-held cities as opposed to simply ejecting ISIS from those areas.
Mattis said the latter change, denying ISIS the chance to escape by enveloping enemy held areas, was critical because it would stop foreign fighters from returning home something he called the "strategic threat."
"The foreign fighters are the strategic threat should they return home to Tunis, to Kuala Lumpur, to Paris, to Detroit, wherever," Mattis said, adding: "We carry out the annihilation campaign so we don't simply transplant this problem from one location."
Previously, military campaigns would allow some ISIS fighters to leave in order to avoid heavier fighting in dense urban terrain with high concentrations of civilians. But Mattis was quick to deny any changes to rules of engagement or an increased tolerance for civilian casualties.
"There has been no change to our rules of engagement, and there has been no change to our continued extraordinary efforts to avoid innocent civilian casualties," he said.
Dunford also credited Trump with making the decision to arm the Syrian Kurds and allowing US advisers to be deployed at the battalion level, which he said has been particularly effective in the fight for Mosul, which he said had led to about 980 Iraqi forces killed and over 6,000 wounded.
On the new delegation of authority, Mattis said "no longer will we have slowed decision cycles because Washington DC has to authorize tactical movements on the ground," an apparent rebuke of President Barack Obama's administration, which was criticized by some military officials for micromanaging tactical decisions in the field.
Brett McGurk, the special presidential envoy for the global coalition to counter ISIS under both Trump and Obama, also cited the increased authority granted to battlefield commanders as having a major impact, saying it had "made a difference in terms of the speed of execution" of the battle plan.
McGurk pointed to a March operation near Tabqa, Syria, where the US commander decided to have US helicopters ferry hundreds of Syrian Democratic Forces fighters behind enemy lines to conduct a surprise attack on ISIS. A US military official told CNN that "there was no way" such a tactical decision would have taken place without direct approval from the White House during the Obama administration.