Reports say Russia’s defence ministry has denied allegations its planes struck US-backed fighters in Syria on Saturday.
The ministry said its air force only targeted Islamic State militants.
It was responding to claims by the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab groups, that six of its fighters were wounded in Russian strikes in eastern Syria.
The SDF is moving towards the city of Deir al-Zour, which pro-government forces, backed by Russian forces, are trying to recapture from IS.
Reports further say on Saturday, the SDF claimed that their forces east of the Euphrates River were targeted by Russian and Syrian regime warplanes.
But on Sunday Russian defence ministry spokesman Maj Gen Igor Konashenkov said Russian planes had only carried out carefully targeted strikes against IS in Deir al-Zour province.
He added that the military had given the US, which supports the SDF, advance notice about its operation.
“To avoid unnecessary escalation, the commanders of Russian forces in Syria used an existing communications channel to inform our American partners in good time,” Gen Konashenkov said.
Deir al-Zour province is the last major IS stronghold in Syria.
The Syrian army and its allies are continuing their advance there, with backing from Russian warplanes.
Earlier this month the military announced that it had broken IS’s siege of the city of Deir al-Zour.
Meanwhile Raqqa, the de facto capital of the “caliphate” proclaimed by the jihadist group three years ago, is under siege by the SDF.