"I will not speculate on the composition of this force or whose control they were under", Lieutenant General Jeffrey Harrigian, a spokesman for US Central Command, said.
Syria is simply not within our nation's sphere of interest, nor is there anything to be gained by continued US military involvement in any of the proxy wars now being waged on its soil.
The US and Russian militaries have de-confliction channels to prevent accidental clashes in Syria and alert each other to movements. The coalition said that the pro-regime forces were "likely seeking to seize oilfields" in the resource-rich Deir Ezzor, while Russian Foreign Minister Sergei Lavrov said on Tuesday the "Americans have taken unsafe unilateral steps". Russia's military said it had nothing to do with the attack and the US accepted the claim.
Lt. Gen. Jeffrey Harrigian says the drone saw the tank "that took a shot at us", and that he believes the U.S. rules of engagement allowed for the tank to be destroyed in self-defense to protect the drone.
At no point, a USA military spokesman said, was there any chance of direct conflict between US and Russian ground forces.
The reports attribute the alleged casualties to a recent United States airstrike and put the figures between 100 and over 600. "I advise you to contact the defence ministry".
More than 200 contract soldiers, mostly Russians fighting on behalf of Syrian leader Bashar al-Assad, died in a failed attack on a base held by USA and mainly Kurdish forces in the oil-rich Deir Ezzor region, two of the Russians said.
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The US Defence Department said the air strikes, which included fighter and ground-attack aircraft and Marine artillery, were launched after as many as 500 attackers waged a coordinated assault on a base housing Syrian opposition forces, along with US military advisers in Deir ez-Zor.
According to reports from the Department of Defense, a Russian-made T-72 Main Battle Tank was destroyed by a drone strike after it attempted to engage Syrian Democratic Forces (SDF) and the coalition advisors working alongside them in Syria on Saturday, one week after a large scales engagement between pro-Assad and SDF troops forces in the region.
A Cossack organization in Kaliningrad posted on social media that one of its members had also been killed. However, he casts doubts on the reports, noting that the whole column, which was alleged bombed out in the USA attack, counted "a bit more than 500 people".
As the main worldwide backer of Syrian President Bashar al-Assad's regime, Russian Federation has committed itself to aiding in the country's reconstruction.
Russian media have reported that in addition to Russian servicemen deployed to Syria, thousands of Russians also fought there as private contractors, most serving with the so-called Wagner group.
While the USA has used private contractors in Iraq and Afghanistan for years, Russian law forbids the hiring of mercenaries or working as one even though Russia has used proxies in eastern Ukraine, where it has backed pro-Moscow separatists since 2014.
On Tuesday, associates of two Russian fighters confirmed to the BBC that they were killed on 7 February.