Russia’s foreign ministry has confirmed that “several dozen” Russian citizens – not regular soldiers – were killed or wounded in a recent battle in Syria.
The statement did not give the date. Previously the Russian government said “probably five” Russians had died in a clash in Deir al-Zour province.
Some reports have said more than 100 Russian mercenaries were killed in US air strikes on 7 February.
The latest Russian statement said no Russian regular forces were involved.
Russian officials generally refuse to give details of Russian “volunteers” involved in the Syria conflict.
Independent media have found evidence of Russian mercenaries fighting for the Syrian government side.
Russia’s official military role mainly takes the form of air strikes, helping President Bashar al-Assad’s forces.
The foreign ministry, quoted by the RIA news agency, described the Russian casualties as “Russian citizens who went to Syria of their own accord for various reasons”. Some were also from other ex-Soviet republics.
The statement did not specify the numbers of dead or wounded, but spoke of “several dozen” casualties, and said the wounded were being treated now in hospitals in Russia.
The US military said US air strikes were launched on 7 February against an attacking force of about 500 fighters, about 100 of whom were killed.
It said the attack was by pro-Syrian government fighters, who were targeting a base held by US-backed Kurdish forces.