The Pentagon confirmed the airstrike, saying Russia was aware that the US-backed SDF and coalition forces were operating in the area.

SDF and Russian-backed Syrian regime forces are conducting parallel but separate offensives against Daesh in the strategic province of Deir Ezzor.
SDF and Russian-backed Syrian regime forces are conducting parallel but separate offensives against Daesh in the strategic province of Deir Ezzor. (Reuters)

Russia knew the US-backed Syrian Democratic Forces (SDF) and coalition advisers were located in the part of Syria's Deir Ezzor that it bombed earlier on Saturday, the Pentagon has said.

The SDF was hit by an airstrike east of the Euphrates River, which the US-led coalition blamed on Russian fighter jets, marking the first such incident during the six-year war in Syria. 

"At approximately 12:30 am GMT (3:30 am local time) September 16, Russian forces struck a target east of the Euphrates River in Syria near Deir Ezzor, causing injuries to coalition partner forces," the Pentagon said in a statement.

"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 statement added that no coalition troops were wounded.

The SDF said the incident happened in Al Sinaaiya area,  an industrial area northeast of the city of Deir Ezzor, about seven kilometres  from the east bank of the Euphrates.    

TRT World's Alican Ayanlar has more on the story from the Turkish city of Gaziantep on the border with Syria.

The SDF is an alliance of Arab and Kurdish forces put together by the US coalition to fight Daesh on the ground in Syria, but is largely comprised of YPG militants with links to the PKK, which the US considers to be a terrorist organisation. 

Turkey, a key coalition partner and NATO ally, also considers the YPG to be the Syrian branch of the PKK, which has waged a war against the Turkish state for several decades.

The Britain-based Syrian Observatory for Human Rights earlier on Saturday confirmed the airstrike, but said it was not clear if it was carried out by Russian or Syrian warplanes.

Moscow has denied the claim that its fighter jets were involved.

US-backed SDF and Russian-backed Syrian regime forces are conducting parallel but separate offensives against Daesh in the strategic and oil-rich eastern province of Deir Ezzor.

Regime troops are waging an assault for the provincial capital, Deir Ezzor city, while SDF fighters battle Daesh further east across the Euphrates River.

A picture taken during a press tour provided by the Russian Armed Forces on September 15, 2017 shows Russian soldiers standing guard in a central street in Syrias eastern city of Deir Ezzor, as locals pass by.
A picture taken during a press tour provided by the Russian Armed Forces on September 15, 2017 shows Russian soldiers standing guard in a central street in Syrias eastern city of Deir Ezzor, as locals pass by. (AP)

Congested Syrian skies 

The SDF say they are not coordinating their operations with the Syrian regime or Russia.

But the coalition says there is a de-confliction line to prevent the two offensives from clashing.

The line agreed between Russia, the regime, the SDF and the coalition runs from the Raqqa province southeast along the Euphrates River to Deir Ezzor.

The skies over Syria have become increasingly congested as the six-year conflict has dragged on, with warplanes from the coalition, the Syrian regime and Russia all carrying out air strikes.

Confrontations between the warplanes have been rare, but in June a US fighter jet shot down a Syrian regime warplane accused of bombing SDF units in the country's north. 

Over 400,000 people have killed and millions displace in the Syrian conflict since 2011. 

Daesh which in 2014 overran swathes of territory across Syria, is seeing its zones of control dwindle even as it claims responsibility for bloody attacks abroad.

Source: TRTWorld and agencies