Russia has denied accusations it bombed US-backed fighters in Syria, saying the US military received advance warning of an air raid targeting ISIL members.

The Syrian Democratic Forces (SDF), a US-supported alliance of Kurdish and Arab fighters, said six of its members were wounded during the Russian-backed Syrian government offensive on Saturday in Syria's northeastern Deir Az Zor province.

The Pentagon on Saturday accused the Russians of deliberately targeting SDF soldiers and coalition advisers.

Major-General Igor Konashenkov, chief spokesman for the Russian ministry of defence, dismissed the claims, saying Russia attacked only Islamic State of Iraq and the Levant (ISIL, also known as ISIS) targets based on multiple-source intelligence on their locations.

"Russian air forces carry out pinpoint strikes only on IS targets that have been observed and confirmed through several channels," state news agency TASS quoted Konashenkov as saying on Sunday.

"In the last few days, Russian surveillance and reconnaissance did not detect a single clash between Islamic State and armed representatives of any 'third force' on the eastern bank of the Euphrates," he said.

Konashenkov added the SDF and American authorities had been sufficiently informed before the air raid.

"To avoid unnecessary escalation, the commanders of Russian forces in Syria used an existing communications channel to inform our American partners in good time about the borders of our military operation in Deir Az Zor," he said.

READ MORE: Pentagon - Russia knowingly hit US-backed SDF in Syria

Franz Klintsevich, a member of the Russian parliament's security committee, said there was no proof supporting the accusations levelled against Moscow.

Deir Az Zor province and its capital city of the same name are regarded as a key strategic prize by both Russian-backed Syrian troops and US-supported fighters.

The area, largely held by ISIL since 2014, has been the site of intense conflict in recent weeks, with pro-government forces advancing under cover of Russian air raids from the west and the SDF approaching from the north.

ISIL once controlled most of the province including Deir Az Zor city, encircling about 100,000 civilians that lived in government-controlled neighbourhoods there.

The armed group has also been pushed out of two-thirds of its former bastion, Raqqa, by the SDF.