Syria’s main Kurdish militia has the distinction of being the only faction in the war-torn country to have the backing of both Russian and US airstrikes.
However, its advances against rebel forces in the north of Syria have rankled Turkey and complicated matters for Washington.
Analysts say the Kurdish People’s Protection Units (YPG) have managed to manoeuvre cleverly amid the political turmoil of Syria, battling Islamic State and carving out a self-proclaimed autonomous territory.
The group has a long-standing detente with the Syrian government and recently has been able to capitalise on Russian airstrikes against rebel factions in Aleppo, in northern Syria.
In the north-east, the US has been backing the YPG with airstrikes against Islamic State since late 2014 and shows no sign of abating.
Meanwhile, the YPG - which espouses a leftist, communitarian ideology - steadily advances across northern Syria, claiming large swathes of territory it dubs Rojava, meaning western Kurdistan.
“The Kurds are now dictating the course of events,” says Aaron Stein, an analyst at the Atlantic Council think-tank. “Turkey is reacting and not setting the tempo.”
Turkey’s leaders have grown increasingly worried about the gains of the YPG, which has ties to the armed Kurdistan Workers’ Party (PKK), a group enmeshed in a conflict with Turkish security forces for more than 30 years.
President Recep Tayyip Erdogan has vowed Turkey will continue to shell YPG positions in Syria and demanded that the US choose between its Nato ally in Ankara and the Kurdish militia.
“The Americans are very upset about what is going on because of the geopolitical headache this is causing,” Stein says.
But US policy is focused on defeating the Islamic State group. As long as the Kurds remain a capable ally in that field, there is no sign Washington will abandon its only reliable ground force in the fight against the extremists in Syria.
Moscow too seems to be comfortable working with the Kurds, who are not making claims on territory Syrian President Bashar al-Assad sees as essential.
The current objective of the YPG seems to be to link up its canton of Efrin, in the far north-west, to its main territory stretching across northern Syria along the Turkish border.
“The only remaining obstacle is the part of the border that is controlled by Islamic State,” says Thomas Pierret, the director of the Centre for the Advanced Study of the Arab World at the University of Edinburgh.
With the air support the YPG has been getting, taking this territory from Islamic State might yet be in reach, he adds - although the amount of firepower needed could also drive out all the area’s civilians.
Turkey is not only watching the Kurds gain, it is seeing the Syrian rebel groups it supports, including Islamist factions, collapse in Aleppo, largely because of the Russian airstrikes.
Worse, the Syrian government - which Turkey wants overthrown - is preparing to place rebel-held eastern Aleppo under siege.
Starving out the opposition fighters could take months or even years, but the fall of the city would be symbolic for al-Assad and would free up troops for other battles.
Emerging as a second symbolic point is the town of Azaz, near Aleppo and just south of the Turkish border. Turkish Prime Minister Ahmet Davutoglu has promised that he will not let Azaz fall to the advancing Kurds.
“I don’t think Turkey can do much,” cautions Howard Eissenstat, an associate professor of Middle East history at St Lawrence University. With Russia flying over Syria, Turkey will not risk a ground operation.
Turkey downed a Russian plane in November, infuriating Moscow, and there seems to be no appetite in Ankara for another direct confrontation.
The YPG may in fact pass on Azaz, which shelters tens of thousands of Arab civilians fleeing the increasingly lethal Russian airstrikes which have also hit hospitals and schools.
“The Kurds might be able to live with that situation where Azaz becomes almost de facto part of Turkish territory,” says Pierret, noting that the YPG can still attack Islamic State and connect its own territories without holding the town.
Turkey has long sought a buffer zone in the area, in part to stem to flow of refugees to the country.
Not having to rule an Arab population that has largely supported the rebels could in fact be “a net benefit” for the YPG, Pierret says.
The other lands the Kurds seek to take from Islamic State are inhabited by many tens of thousands of Sunni Arabs and it remains unclear how they would govern - assuming the civilians are not driven out by airstrikes.