"They have been provided with assistance for the return to Russia where, to our knowledge, they are receiving treatment in various medical institutions," a ministry statement said.

On Thursday, Russian Foreign Ministry spokeswoman Maria Zakharova said five Russian nationals were preliminarily confirmed to have been killed in Syria in the clash with the U.S.-led coalition.

The ministry denied the relation of the killed and the wounded with the regular Russian armed forces.

"There are Russian citizens in Syria, who went there on their own accord and with different goals," the statement said, adding that it was not the task of the ministry to assess the legitimacy of such decisions.

The Russian Defense Ministry said in a statement earlier this month that a pro-Syrian government militia unit conducted a reconnaissance and search operation on Feb. 7 in the vicinity of an oil refinery in the province of Deir al-Zour to identify and destroy a bandit group responsible for shelling government troop positions, and came under fire from the U.S.-led coalition and its local allies.

The coalition claimed that it carried out airstrikes against "Syrian pro-regime forces" that launched an "unprovoked attack" on Kurdish-led Syrian Democratic Forces' headquarters and killed an estimated 100 militia.

Russia started participating in the anti-terrorist operation in Syria in September 2015 at the invitation of the Syrian President Bashar al-Assad, predominantly with missile strikes in support of the Syrian army.