It was the sort of deadly confrontation many had long been feared. Americans and Russians traded fatal force inside Syria, bringing the two former Cold War adversaries into direct military conflict.
Yet although the clashes earlier this month around Deir Ezzor killed perhaps dozens of Russians, the aftermath has been marked not by escalation but by Moscow’s reticence to highlight an awkward fact of its Syrian war: growing reliance on a mercenary army.
The result is a cloud of confusion about what happened and who was responsible for an assault on the Conoco oilfield, a lucrative and strategic prize now held by US allies.
"They are clearly not interested or willing in escalating on their behalf," said Michael Hanna, a Middle East expert at the Century Foundation.The United States has confirmed that a force loyal to Bashar al-Assad and supported by artillery attacked a Syrian Democratic Forces base manned by Kurdish troops and American advisers on February 7 around Deir Ezzor.
Its special forces responded by calling in artillery strikes, ground attack jets and B-52 bombers, which all but wiped out the "battalion sized force" in front of them.
The Russian defence ministry initially insisted it had no servicemen in the eastern province of Syria.
But details of the operation have gradually emerged, along with growing anger inside Russia that its citizens' deaths are being quietly ignored as inconvenient bad news ahead of President Vladimir Putin’s run for re-election next month.
The Conflict Intelligence Team (CIT), a respected group of Russian online researchers, has named 10 citizens killed in the US air strikes.
"The mercenaries weren't actual Russian soldiers, and moreover the operation was allegedly not reported to or approved by Russia's command in Syria," said Kirill Mikhailov, a researcher with the group. "The ministry of defence in particular tried to distance itself from the incident, saying there were no Russian soldiers there and that the local militias acted without Russian approval."
The foreign ministry finally admitted on Thursday that five of its citizens were among the dead but Mr Mikhailov said medical sources inside Syria suggested as many as 100 may have been killed.
He and other analysts believe the dead worked for the Wagner group, a Russian military contractor originally established to fight for Moscow in eastern Ukraine. CIT has reported it is linked to Yevgeny Prighozin, nicknamed "Putin’s chef" for his close ties to the president and who was indicted by the US last week for his alleged role in funding an internet troll factory.
Although the use of such arms length fighters allows Moscow to pursue its interests in Syria while offering a measure of deniability, there are questions about Wagner’s real motives. Is it working for the interests of its Russian owners undercutting the Kremlin’s aims of shoring up the Assad regime?
Last year, the Associated Press reported that a Russian company linked to Wagner had been promised 25 per cent of profits from oil and gas fields captured from militant control.
"This move against majority-Kurdish SDF actually erodes whatever trust Russia might have won with the Kurds by bombing some of their targets during the anti-ISIS operation," said Mr Mikhailov, adding that it hampered Mr Putin’s need to bring the SDF to the negotiating table before the March 18 election. "Putin must make up for failing to deliver on Russians' quality of life by projecting himself as foreign policy winner or peacemaker."
If the death toll estimates are true it would eclipse previous casualty numbers, making it more difficult for Mr Putin to continue to argue his campaign has been largely bloodless.
Relatives of the dead are demanding to know what happened.
"I want everyone to know about my husband, and not just about my husband, but about all the guys who died there so stupidly," Yelena Matveyeva told the regional news site Znak.com. "They sent them like pigs to the slaughter."
The Americans are either none the wiser or not letting on how much they know.
Jim Mattis, the US defence secretary, has promised to get to the bottom of what happened but has so far stopped short of accusing Moscow of orchestrating the assault.
Flying back to Washington after a week long tour of Europe, Mr Mattis chose his words carefully.
"I understand that the Russian government now is saying that some of their not-military forces, contractors, were involved in that still unexplained attack," he said.
"But they took directions from someone. Was it local directions? Was it from external sources? Don't ask me, I don't know.
"But I doubt that 250 to 300 people, all just excited on their individual self, suddenly crossed the river in enemy territory, started shelling a location and manoeuvring tanks against it."
Whatever the truth hidden in the fog of war, it raises the prospect of further clashes between Russia and the US as the conflict in Syria enters a new phase following the defeat of ISIL, and with Israelis, Americans, Russians, Iranians and Turks all operating inside Syria.
"My worry is not there is going to be an intentional escalation but that mistakes happen on the battlefield and these kinds of incidents can take on a logic of their own," said Mr Hanna. "It hasn't in this case, thankfully, but it's dangerous."