Russian Federation has acknowledged that five of its citizens were killed in a US-led coalition bombing in the eastern Deir Ezzor province after they were part of a group of pro-regime combatants which led an attack on positions held by the Syrian Democratic Forces.
As Russia's Defense Ministry announced earlier, the Syrian militia fighters came under the coalition's strikes in the province of Deir ez-Zor on February 7 due to actions uncoordinated with the Russian military.
The contractors, mostly ex-military, carry out missions assigned to them by the Russian military, the people familiar with the deployment said.
Dozens of Russian and CIS citizens were hurt in a recent skirmish in Syria and some were killed but these were not Russian troops, Russia's Foreign Ministry said on Tuesday.
Moscow has provided no details of what the mercenaries were doing, but accounts of the operation have emerged in interviews with family members.
The Russian government is reviewing a bill that would make private military companies legal, in order to clarify the now murky status of mercenaries engaged in conflicts overseas.
The mercenaries were apparently working for a private Russia-based military company called the Wagner Group.
Relatives of the dead are demanding to know what happened.
The military began a partial withdrawal from Syria in December on orders by President Vladimir Putin, soon after Syrian troops completed the destruction of the main Islamic State terrorist forces in the war-torn country.
An armed clash earlier this month in which United States strikes may have killed more than 200 Russian mercenaries attacking American-backed forces inflamed a standoff between Moscow and Washington in Syria.
"Was it local direction? 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 maneuvering tanks against it", he added. "Was it from external sources?Don't ask me.I don't know", the USA defense secretary said.