A Russian fighter was killed and several others wounded in Syria's northern province of Aleppo on Monday, a war monitor and a Kurdish security source said.
The Syrian Observatory for Human Rights, which monitors conflict in Syria, said the Russian casualties occurred when their convoy was hit by Turkish shelling.
The security source said the attack came from an area where Turkish troops are deployed and that the wounded were treated in Afrin, an area controlled by Turkish-backed troops.
The Russian defense ministry did not immediately respond to a Reuters request for comment. Russia intervened in Syria's conflict in 2015, using air strikes and deploying advisers as well as military police to help Syrian President Bashar al-Assad retake territory from rebels, some of them backed by Turkey.
Turkish shelling in Syria
A Turkish defense ministry official said on Monday reports that Turkish forces had shelled positions in Aleppo's northern countryside and hit Russian armored vehicle were "untrue."
The Syrian National Army, an opposition faction backed by Turkey which controls the area near where the attack took place, did not respond to a Reuters request for comment.
A video published by Ronahi TV, a station affiliated with the Kurdish-led autonomous administration in northeast Syria, showed men in fatigues transporting at least two men on stretchers into a Russian helicopter.
The helicopter is then seen taking off. It was not immediately clear where the helicopter was flying to, who the apparently wounded men were or what was being said in the video.
Syria's 12-year conflict has carved the country into complex zones of control where outside actors - including government allies Russia and Iran, as well as Turkey and the United States - hold significant sway.
In 2015, Turkey shot down a Russian warplane near the Syrian border but Ankara and Moscow have since mended relations. They coordinate joint patrols in northern Syria and Russia is trying to mediate between the governments of Turkey and Syria.