Kurdish forces that were until last week allied with the US have reached a deal for assistance with the government of Syrian President Bashar al-Assad, which is backed by Russia.
Syrian regime troops are now moving to the Turkish–Syrian border as Kurdish-led forces come under assault by Turkey's armed forces and their proxies.
The Kurdish-led Syrian Democratic Forces (SDF) turned to Russian-backed Syria after US President Donald Trump decided to withdraw pockets of American troops deployed in northeastern Syria. Trump did so following a call with Turkish President Recep Tayyip Erdogan, effectively allowing the Turkish military incursion to begin.
Trump's move has drawn widespread criticism, including from the president's Republican allies, with many accusing the US of betraying the Kurds.
The SDF, funded and armed by the US, had been the most effective western-backed force fighting ISIS. It played a huge role in the terror group's eventual territorial defeat. The SDF also was responsible for thousands of ISIS members and supporters being taken prisoner during the conflict.
Fears that ISIS prisoners could break free and regroup in the chaos of the Turkish invasion seemed to be realized Sunday when Kurdish officials said that hundreds of relatives of foreign ISIS members had escaped from a camp in northern Syria.
In an article for Foreign Policy magazine, SDF commander in chief Mazloum Abdi said the Kurds had no choice but to give up the self-rule they had established and partner with Assad and, by extension, Russian President Vladimir Putin.
"We believe in democracy as a core concept, but in light of the invasion by Turkey and the existential threat its attack poses for our people, we may have to reconsider our alliances. The Russians and the Syrian regime have made proposals that could save the lives of millions of people who live under our protection. We do not trust their promises. To be honest, it is hard to know whom to trust," he wrote.
"But if we have to choose between compromises and the genocide of our people, we will surely choose life for our people."
Turkey views parts of the SDF as terrorists. They see them as indistinguishable from Kurdish separatists who have fought an insurgency inside Turkey for decades.
Erdogan said the aim of the Turkish military incursion was to establish a 30-kilometer "safe zone" inside Syria that would allow Turkey to repatriate the millions of Syrian refugees in Turkey.
However, the Syrian regime moving to take control of this area means that it is highly unlikely the refugees will be able to return. Tens of thousands of civilians have also been displaced by the Turkish military operation, with aid agencies warning of a growing humanitarian crisis.
On Monday the European Union condemned the Turkish incursion. President Trump tweeted that "big sanctions" were coming for Turkey.
In the same tweet, he appeared to suggest that the Kurds, who up until last week were America's major ally in the region, were deliberately releasing ISIS prisoners in order to convince the US to redeploy troops.
Trump has spent the days since his phone call with Erdogan trying to play down US involvement in the Syrian civil war and the extent of the alliance with Kurdish fighters. He said, “they didn’t help us in the Second World War, they didn’t help us with Normandy."