The U.S.-led coalition battling Islamic State (IS) militants in Syria says the Russian military has struck forces backed by Washington in the war-torn country, injuring several allied fighters.



The assertion came hours after the Syrian Democratic Forces (SDF), a U.S.-backed Kurdish-Arab militia in Syria, accused Russian jets of bombing its forces in Deir al-Zor Province on September 16, injuring six of its fighters in the last major IS stronghold in Syria.



"Russian munitions impacted a location known to the Russians to contain Syrian Democratic Forces and coalition advisors. Several SDF fighters were wounded and received medical care as a result of the strike," the coalition said in a statement.



The statement added that coalition advisers who were present "were not wounded as a result of the Russian strike."



The United States and Russia back separate military offensives in the Syrian war, both of which are advancing against IS forces in the east of the country near Iraq.



Russia and Iran back Syrian President Bashar al-Assad in the country's six-year-old war, while the United States and Turkey support various rebel groups opposed to the Damascus government.



IS fighters, who captured large swathes of Syrian territory in 2014, are opposed by all sides and are being driven from most of their strongholds by the separate government and rebel campaigns.



Washington and Moscow have largely stayed out of each other's way in their fight against IS in Syria, with the Euphrates River frequently serving as a dividing line.



The commander of the U.S.-led coalition, Lieutenant General Paul Funk, said in the September 16 statement that coalition officials "are available and the de-conflictation line with Russia is open 24 hours a day."



"We put our full efforts into preventing unnecessary escalation among forces that share ISIS as our common enemy," Funk said, using an alternate acronym for the extremist group.



The statement added, "Coalition forces and partners always retain the right of self-defense."



There was no immediate comment from officials in Moscow on the incident, though AFP quoted a Russian military spokesman in Syria earlier in the day as saying that Russia was not responsible.



"This is not possible. Why would we bomb them?" Igor Konashenkov was quoted by AFP as saying earlier on September 16 at the Hmeimim base on Syria's coast.

With reporting by Reuters, AP, and AFP