U.S.-backed forces fighting in Syria accuse Russia of conducting airstrikes on them

BEIRUT — The U.S.led coalition fighting the Islamic State in Syria said Saturday that its partner forces have been attacked by Russian warplanes, escalating tensions on one of the country’s most complex battlefields.

The coalition said in a statement that an early morning airstrike targeted positions used by the Syrian Democratic Forces, or SDF, a Kurdish-dominated militia backed by Washington, as well as the international advisers supporting them in a weeksold offensive to dislodge Islamic State militants from the eastern province of Deir al-Zour.

As the Islamic State loses territory across Syria and Iraq, oil-rich Deir alZour has become a hub for the group’s senior leaders.

Stretching along the eastern border with Iraq, it has also emerged as a geopolitical battleground for forces trying to support or thwart Iranian attempts to secure supply routes stretching from Beirut to Tehran.

The U.S.-led coalition intervened in Syria and Iraq in 2014 to halt the Islamic State’s conquest across swaths of both countries. Iran and Russia’s involvement dates back to the early months of the civil war that followed Syria’s 2011 anti-government uprising, bankrolling and later militarily supporting President Bashar al-Assad’s forces as part of a broader attempt to maintain key allies across the region.

In Deir al-Zour, the two military groups now find themselves fighting a common enemy. SDF fighters have advanced against Islamic State positions on the eastern bank of the Euphrates River in recent weeks, while forces allied with Assad’s government have scythed through the extremist group’s territory from the western side, entering Deir Ezzor city and bringing the rival coalitions to within several miles of each other.

Saturday’s attack marks the first time that the U.S.and Russian-backed forces have clashed directly, signaling what appeared to be a growing willingness for Russia to protect its proAssad allies as they consolidate control over strategic parts of the province.

Although the Pentagon, SDF, Russia and Syria have agreed a line of “physical separation” between their parallel offensives, rising tensions have raised the specter of open clashes.

“Coalition officials are available and the deconfliction line with Russia is open 24 hours per day,” said coalition commander Lt. Gen. Paul Funk.