American proxy militias in eastern Syria engaged in heavy clashes this week, potentially undermining the US presence in the country and adding another twist to the 12-year, multi-faction conflict.
The fighting, mainly in Deir Ezzor governorate between Kurdish and Arab militias that left about two dozen people dead, plays to the advantage of Iran, Turkey and Russia, observers said.
The three powers have also carved out zones of influence in Syria and comprise the so-called Astana grouping.
They want to see the US exit Syria, leaving the scene solely to them.
“We are seeing the result of territorial competition between highly pragmatic militias over loot and resources,” a source in the US-supported, Kurdish controlled administration of eastern Syria told The National.
Since Syria was carved out of the remnants of the Ottoman Empire in the 1920s, the east has been a centre of land disputes between Arabs and Kurds, exacerbated by ethnic tensions.
In the 1980s, thousands of Kurds fled Turkey to Syria, to escape fighting between the authorities and Kurdish separatists. This raised Arab-Kurdish tensions in Syria.
The fighting this week pits the Kurdish People’s Protection Units (YPG) against the Sunni Arab Deir Ezzor Military Council.
The YPG dominates the Syrian Democratic Forces, a military grouping set up by the United States in 2014 to fight ISIS. With money and weapons, the grouping later attracted the Military Council to its side, as locals rallied against the ultra-violent ISIS occupation.
But YPG gunmen this week arrested Abu Khawla, the Military Council’s commander, intensifying fighting between the two groups, Arab and Kurdish sources say.
On Wednesday, YPG-led infantry columns moved against the Military Council’s stronghold in a group of villages and towns near a road running parallel to the Euphrates River.
The assault, which made some headway, would not have been possible without the go-ahead from the US military in the area, the Kurdish source says.
“Abu Khawla has been expanding his road blocks and opening channels with everyone: Iran, the [President Bashar Al Assad] regime, and maybe even ISIS,” the source said.
“He has been beating the YPG at its own game.”
Over the last decade, eastern Syria, the centre of the country's oil production, was taken over by the YPG, and its predecessor, the Democratic Union Party (PYD).
The PYD is a branch of the Kurdistan Workers Party (PKK), a Marxist-Leninist Turkish group who for decades has fought Ankara.
Starting in 2012, Kurdish militias acquired Arab tribal territory in eastern Syria from the Free Syrian Army, a now all-but-defunct grouping of anti-Assad rebels, and later from Islamist militant groups who included Al Qaeda-linked Al Nusra Front, and later ISIS.
During Syria's civil war, survivors of the Free Syrian Army fled to the north of the country, or were moved there as part of Russian-supervised surrender deals with Damascus. There, they joined Islamist groups armed and funded by Turkey, further exacerbating Kurdish-Arab tensions.
The Free Syrian Army, renamed the Syrian National Army, ousted Kurdish militias from several Kurdish-majority areas on the Turkish border, in operations backed by the Turkish army and strongly condemned by the US.
Since then, the US has struggled to maintain order in the east of the country, amid a simmering ISIS insurgency.
With support from the US, the YPG has sought to placate Arab Sunni tribes by giving their members positions in the Syrian Democratic Forces, as well as civilian administration positions.
Abu Khawla, however, has been acting independently, seeking to change tribal leaders who had aligned with the YPG, and consolidate his power base in Deir Ezzor.
He competed with the YPG over the spoils of the war economy, particularly oilfields and passage fees on commercial land routes, sources say.
Before the civil war, he was an obscure figure, one of the millions of rural inhabitants of the east who could barely make ends meet.
The war broke out after the authorities used violence to suppress the peaceful pro-democracy protest movement in 2011, which included Kurds, who had long felt marginalised by Damascus.
But as Syria descended into a brutal civil conflict, Kurdish militiamen in the east, mostly trained by the PKK at its northern Iraq headquarters, supported the authorities in cracking down on the protest movement.
They later helped loyalist forces capture rebel-held areas, especially the eastern part of the historical metropolis of Aleppo.
Despite this, the Kurdish militias have failed to reach a deal with Mr Al Assad for autonomy and to keep their arms.
How many gains the YPG will be able to make in Abu Khawla's core territory depends on the ability of the Military Council to rally Arab tribes, says a Syrian officer who had defected from the regime and knows the area.
“Regardless of the outcome, Arab resentment in the east will mount,” he says. “Iran will be flying from joy.”
He pointed out calls by Nawaf Al Bashir, an Iranian-backed tribal figure, on Arab tribes in Deir Ezzor to defend against the YPG onslaught.
“It is a shame if you allow Kurdish hegemony on your areas,” Mr Al Bashir said in a voice note to a tribal WhatsApp group. “Beware of the Kurdish project. Expel them from your homeland.”