US-backed fighters in Syria said they came under attack on Saturday from Russian jets and government forces in Deir Ezzour province.
The Kurdish-led Syrian Democratic Forces (SDF) alliance, which is fighting with the US-led coalition against ISIL, said the strikes wounded six of its fighters.
Washington and Moscow support separate offensives in the Syrian conflict — with both sides advancing against ISIL militants in the eastern region that borders Iraq.
"Our forces east of the Euphrates were hit with an attack from the Russian aircraft and Syrian regime forces, targeting our units in the industrial zone," the SDF said.
The alliance accused the Syrian government of trying to obstruct its fighters. Such attacks "waste energies that should be used against terrorism ... and open the door to side conflicts", it said.
There was no immediate comment from Moscow or Damascus.
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The proximity of the offensives by the Russian-backed Syrian army and the US-backed SDF have at times raised fears of clashes between the two sides that could stoke tensions between Moscow and Washington.
The assaults have converged on ISIL from opposite sides of the Euphrates river, which bisects oil-rich Deir Ezzour, ISIL's last major foothold in Syria.
Syrian troops fighting with Iran-backed militias have closed in from the west since last week, while the SDF advances from the east.
Russian and US battles against ISIL in Syria have mostly stayed out of each other's way, with the Euphrates often acting as a dividing line. Talks have been under way to extend a formal demarcation line, officials have said.
The US-led coalition has said the SDF does not plan to enter Deir Ezzour city, where the Syrian army recently broke an ISIL siege that lasted three years.
Still, in June, the SDF accused the Syrian military of bombing its positions in Raqqa province and the United States shot down a government warplane in Syria's crowded airspace.
Ahmed Abu Khawla, commander of the SDF's Deir Ezzour military council, said Russian or Syrian fighter jets flew in from government territory before dawn on Saturday.
The warplanes struck as the SDF waged "heated and bloody battles" in the industrial zone on the eastern bank, seizing factories from ISIL militants, he said.
"We have requested explanations from the Russian government," he added. "We have asked for explanations from the coalition ... and necessary action to stop these jets."
The Syrian Observatory for Human Rights, a Britain-based war monitor, said coalition planes had pounded the same industrial zone overnight to help SDF advances against ISIL.
The strikes came a day after Abu Khawla said his fighters would not let Syrian government forces cross the Euphrates.
On Friday, he warned the army and its allies against firing across the river, something he said they had done in recent days.
The Russian foreign ministry said units of the Syrian army had already crossed, however.
A senior aide to Syrian president Bashar Al Assad said the government would fight any force, including the US-backed alliance, to recapture the entire country.
"I'm not saying this will happen tomorrow … but this is the strategic intent," Bouthaina Shaaban said.
