"During a recent military clash, in which servicemen from the Russian Federation did not participate in any way, citizens from Russia and (former Soviet) countries died," the Russian Foreign Ministry said in a statement on Tuesday, according to Military.com.
The ministry further stressed that the combatants were not Russian servicemen and that no Russian military equipment was involved in the fighting.
It gave no date or location for the clash, but said the wounded Russian citizens had received help to return home and were receiving medical treatment.
The fighters had traveled to Syria “of their own accord and for a variety of reasons”, the ministry said, although it did not identify any of the dead or wounded by name.
“It is not the place of the foreign ministry to assess the legality and legitimacy of their decisions,” it added.
The announcement came shortly after reports that scores of Russians fighting alongside pro-Syrian forces against terrorists were killed by a US-led coalition airstrike in Deir ez-Zor, in eastern Syria, on February 7. Moscow dismissed those reports last week as “classic disinformation”.
The airstrike marked the first time Russians have died at the hands of the US in Syria since the Kremlin entered the conflict on the side of President Bashar al-Assad in 2015.