In the third part of our series looking at the conclusion of the 21st century’s most devastating conflict, we examine the role of Kurdish militants

Throughout seven years of war, the Kurds of Syria’s north have been a wildcard. Their loyalties have remained uncertain and their push for autonomy buffeted by a raging conflict that has consumed almost all before it.

As a showdown nears in the north-west of the country, home to a prominent Kurdish enclave until earlier this year - and now central to the outcome of the war - the Kurds are quietly renewing their claim. Dozens of Kurdish militants who had fought with US forces in the fight against Islamic State have now allied with Syrian regime forces in Idlib province for what is likely to be the war’s final, bloody battle.

The presence of the Kurds in the fight for Idlib adds a new dimension to a clash that has drawn in every player in the long, savage war. The alliance has been kept under wraps both by Syrian officials, who have been wary of Kurdish ambitions throughout the war, and by Kurdish forces themselves, who remain nominally allied to Washington in the fight against Isis.

A last-ditch diplomatic attempt to avert a fight for Idlib province, where up to 3 million people are crammed into over-stretched towns and cities, is being held in Tehran on Friday. Russia and Iran, both backers of the Syrian regime, and Turkey, a backer of many groups who stood against the Syrian leader, will attempt to thrash out a deal that prevents what aid agencies say will be a bloodbath if, as expected, a full-scale assault is launched.

Facebook Twitter Pinterest Iran’s president, Hassan Rouhani, is meeting Turkish president, Recep Tayyip Erdoğan, and Russian president, Vladimir Putin, in Tehran to discuss the future of Idlib. Photograph: Don Emmert/AFP/Getty Images

On the ground, there is little hope that diplomacy will deliver an outcome. Speaking of global leaders, Amin Azzam, an anti-Assad fighter from the town of Jisr al-Shughour in Idlib, said: “They have failed us for five years. Why would they save us now?”

To the south of the city, a small number of Kurds have gathered with Syrian forces and Iranian-backed militias to await orders. The men are believed to be members of the Syrian Democratic Forces, part of an alliance of Arabs and Kurds raised by the US to take on Isis in the north-east.

With that fight now largely over, the SDF remain bitter at being ousted earlier this year from the town of Afrin in Idlib by Turkish-led Arab forces who had been raised to fight Assad. That defeat left the Kurds without a stronghold in an area in which they had been historically strong and strategically relevant. It also shifted the loyalties of many.

Kurdish leaders say avenging the loss of Afrin remains a priority. Aldar Khalili, a leader of a Syrian Kurdish political bloc, said Kurds would readily deal with Assad to win back the town.

“As of now there aren’t any movements toward sending the forces in Rojava (north-eastern Syria) to the liberation operations in Idlib alongside the Syrian government and Russian forces,” he said. “But we have shown our readiness to go into negotiations with the Syrian government to clear all parts of Syria from the Isis, jihadis and terrorist groups backed by Turkey.”

Another Kurdish leader said small numbers of SDF members had made the long, difficult journey to join Syrian forces. “It’s symbolic on one level and strategic on another. This means we need the regime. There is a partnership growing, but we need to get our pound of flesh from them.”

Afrin was attacked by Turkey and its proxies after the US said it would help raise a permanent border force in the north-east, which Turkey feared would strengthen Kurdish ambitions towards eventual sovereignty. The move would have implications for Ankara’s ongoing war with Kurdish militants inside its own borders.

Facebook Twitter Pinterest A Kurdish girl who lives in Cyprus, stands with her face painted during a protest against the Turkish offensive targeting Kurds in Afrin, Syria. Photograph: Petros Karadjias/AP

Containing Kurdish ambitions, and even preventing a consolidation in Syria, has been central to Ankara’s projection in Syria in the past two years of war. Chasing Kurdish forces from Afrin allowed Turkey to boast that there was no Kurdish enclave along its border west of the Euphrates river. Just as potently, it allowed the Kurds to claim they had been betrayed by a fickle ally.

When the city was under attack, the SDF’s calls for US support were rebuffed. Allies in one corner of the country, they were abandoned in another, with Washington’s already strained relationship with Ankara more important than its bond with Kurdish leaders.

The episode brought the alliance to breaking point. Four Kurdish officials have told the Guardian in recent months that anti-Isis operations have all but stopped. “Those we are carrying out sometimes don’t involve the Americans at all,” said one senior figure. “There is not the trust there was and they should not be surprised if we look after ourselves.”

A senior regional intelligence source said US military leaders have told the SDF that they would not accept their members participating in the Idlib operation, alongside Syrian forces and their Iranian allies.

“If they go, they’ll be without uniforms or flags. They’ll try to look like Syrian troops,” the source said.

Facebook Twitter Pinterest The capture of Afrin, celebrated by Turkish-backed Free Syrian Army fighters, angered Kurds. Photograph: Aref Tammawi/EPA

Khalil said their expulsion from Afrin changed the equation for the Kurds. “The situation in Afrin can’t go on like this and as the coalition of political parties who believe in future democratic Syria, we are ready to go into the negotiations with the Syrian government. We want to build a future democratic Syria that includes every community within the Syrian society equally and we are ready to participate not only in terms of the military but politically and economically.”

In Afrin, local woman Arin, 31, said a low-level insurgency against Turkish forces and its allies continued ahead of the expected Russian-led air assault. “The situation in Afrin is bad and there are random arrests of Kurds with allegations that people are part of the YPG ( a group aligned to the Turkish militant organisation the PKK). “We hear about attacks on the checkpoints of the armed groups controlling the city and there are assassinations every week carried out by the youth who defended the city before it was invaded.”

Afrin remains a focal point of Kurdish resentment and an incentive for many to deepen their engagement with the regime.

“The armed men who are controlling the city are mostly from the areas that were lost to the government like Ghouta, Daraa and other areas,” said Arin. “It was them who changed the dynamic here, not us. We as Kurds were happy here until they fought us. If they fight us, they can expect vengeance. Blood brings blood.”