Two Syrian Kurds were shot dead by a former member of the Free Syrian Army (FSA) last weekend, in what the executioner said was a response to an incident last month in which the Kurdish People's Protection Units (YPG) killed around 50 FSA fighters and transported them back to Kurdish territory in an open-top trailer.
Tensions have flared as images of both incidents — which could not be independently verified — circulated on social media over the weekend and into Monday, until the FSA-aligned rebel group Jaysh al-Thuwar disavowed the alleged murder of the Kurdish civilians as a "crime" by a disgruntled former FSA fighter.
"The offender was fired by the rebels a month ago," the group said in a statement published on its website, calling the incident "a false military operation."
The incident is symbolic, however, of the mutual distrust that continues to cast a shadow over the Kurdish-Arab relationship in northern Syria.
"I think this is an individual act by the perpetrator. However some groups want to take credit for it and present as a revenge act for killing their members last month," Mutlu Civiroglu, a Syria and Kurdish affairs analyst, told Business Insider last week.
The incident comes as the US has tried to bring Arab and Kurdish forces together to fight the Islamic State, threatening to add new complications to that all-important battle.
"Amnesty International has in seven months issued two major reports highlighting allegations of war crimes by rebel and Kurdish forces in northern Syria," Hassan Hassan, a Syrian journalist and resident fellow at the Tahrir Institute for Middle East Policy, wrote earlier this week in The National.
He continued: "The two reports are related to a secondary conflict brewing between Arabs and Kurds from Hasakah to Qamashli to Aleppo, which could easily spin out of control and add to the many conflicts that already plague the country."
Kurdish and Arab fighters have a long history of mutual distrust that peaked between 2012 and 2013, when the Kurdish People's Protection Units (YPG) battled FSA-aligned rebel groups for control over the Syrian city of Ras al-Ayn.
Those tensions have reemerged over the past eight months. The YPG-controlled neighborhood of Sheikh Maqsood has come under siege by both Syrian government forces and the rebels, with reports emerging that the rebels have committed war crimes against the neighborhood's Kurds.
In March, an intense battle between Kurds and rebels in Aleppo punctured the relative calm that had been forged by the cessation-of-hostilities agreement brokered by the US and Russia one month earlier.
The rivalry has put the US in a difficult position. The YPG has proven to be the most effective force fighting ISIS on the ground in northern Syria, but the territorial expansion their victories have afforded them is vehemently opposed by Turkey, an important US ally and member of NATO.
Ankara views Kurdish demands for autonomy as a threat to Turkey's sovereignty. It backs many of the rebel groups that have clashed with the YPG.
Complicating the situation further is the High Negotiations Committee's (HNC) insistence that it should be the only opposition group represented at peace talks in Geneva, where multiple attempts to forge a political solution to the more than five-year war have failed. The HNC is a Saudi-backed coalition of Syrian opposition groups created in Riyadh in December 2015.
Turkey has also objected, citing the Kurdish insurgency it is battling in its southeast.
The US-backed Syrian Democratic Forces (SDF) were supposed to alleviate Turkey's anxiety by incorporating some Arab and Turkmen groups to offset Kurdish influence. But the SDF was established by members of Euphrates Volcano — a coalition that included certain FSA factions but was dominated by the Kurdish YPG — and has since clashed with the FSA's 13th division near the strategically important Azaz corridor.
"The US may not want to jeopardise its relationship with a force that has helped it win key tactical battles against ISIL in Syria, but the unconditional support for the YPG is irresponsible because it creates unnecessary conflicts and undermines the long-term war against extremists," said Hassan, who cowrote "ISIS: Inside the Army of Terror."
Not everyone would agree that the US's support for the YPG is "unconditional." And the case could be made that the US decision to gamble its relationship with Turkey — which has been accused repeatedly of turning a blind eye to ISIS' illicit activities — in favor of a closer relationship with the fiercely anti-ISIS YPG was a strategic move.
Still, Washington's insistence that supporting the group is key to defeating ISIS was complicated in February, when YPG forces further west appeared to be actively coordinating with Russia to recapture territory taken by anti-Assad rebels near Azaz.
As Hassan noted, because one of the YPG's primary goals is to expand its territory in northern Syria by linking its Afrin canton with Jarabulus — and because it is more "anti-ISIS" than "anti-Assad" — the group is viewed suspiciously by Turkey and Sunni opposition groups in Syria.
"I’ve argued all along that empowering the YPG without doing the same for the Sunni Arab opposition would create an acute power imbalance in northern Syria," Middle East expert Charles Lister wrote on Twitter last week, noting that the "imbalance may spark a conflict that could outlast" the one between the regime and the opposition.
"This position has nothing to do with being pro or anti anyone," Lister said. "It’s merely the result of assessing broader dynamics in Syria's north."
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