For nearly five years of war, the Syrian border town of Azaz had been little more than a staging point. Opposition fighters used it to receive supplies from the main crossing three miles north, and casualties of the brutal conflict were sent the other way to hospitals inside Turkey.

Nothing changed when Islamic State made Azaz one of its main hubs for six months from mid-2013. The supplies kept coming and the wounded continued to leave, even as the struggle for the north slowly changed hue from homegrown insurrection to a conflict fuelled by many international agendas. The gateway remained just that – until a fortnight ago, when the Kurds of northern Syria moved towards it.

Since then, Azaz has been transformed into ground zero of the war for the north of Syria. Its fate has implications far beyond, with Turkey, especially, now more heavily invested – and exposed – to the region’s shifting dynamics than at any point since its leaders swung behind the Syrian opposition in the summer of 2011.

What becomes of Syria could well be determined in the border areas around Azaz, where a Game of Thrones-like cast of players is vying for supremacy over lands that stretch south to the ancient city of Aleppo, and north beyond the Turkish frontier, over which Ankara now has less control than at any point since the modern state of Turkey was formed.

In the war rooms of southern Turkey, officials from Arab states and the west say they have never seen their hosts more agitated. The anger started in early February, when Russian jets began blitzing opposition positions between Aleppo and Azaz, which had been supported by Ankara.

The stated Russian target was Isis. However, its positions are well to the east of the areas being bombed, which were exclusively the communities that host Syrian opposition fighters, a mix of Islamist and non-ideological groups.

As the Russian bombs rained down, tens of thousands of refugees fled to Azaz, where they remain camped out in bombed buildings or under olive groves near the border fence. More important for Turkey, though, ground forces allied to the Assad regime started manoeuvring around Aleppo.

Members of a Syrian opposition group attack the headquarters of Assad regime forces in the villages of Nubul and al-Zahraa in Aleppo, Syria on 12 February 2016. Photograph: Anadolu Agency/Getty Images

Lebanese Hezbollah led the charge, along with Shia militias from Iraq and Afghanistan, and the Syrian army. Also on the move, for the first time in this part of Syria, were Kurdish units of the YPG militia, whom Turkey sees as no different from the insurgent PKK in south-eastern Turkey, with which it has been fighting for four decades.

“The alarm was uncontained,” said one senior western official. “The Kurds have really tried it on this time and Turkey is beside itself. They keep saying to us that we have created this by partnering with the Kurds in the fight against Isis and by looking the other way as the Russians run rampant.”

Turkey’s anger has been simmering since late 2014, when the US began using the YPG in north-eastern Syria as a ground force to fight Isis, while its fighter jets, along with those of a coalition it assembled, bombed the group from above.

To the US, and to Nato, of which Turkey is a member, the rise of Isis marked a grave threat to the socio-religious makeup of the Middle East and to global security. The Kurds were an asset, not a hindrance. After all, they had proved their worth in August 2014, crossing from Syria into northern Iraq to lead 40,000 Yazidis down from Mount Sinjar, where they had been besieged by Isis. And, with the Iraqi army having abandoned Mosul and northern Iraq, the Syrian army having fled the east of its country, and no western army interested in returning to the region, who else could help shift Isis from its strongholds?

Turkey was far from convinced. It refused to let US jets use its Incirlik air base to launch attacks against Isis and showed no interest in taking part itself. The Kurds were a far bigger threat, it insisted. And, as a Nato member, its allies were treaty-bound to protect it.

Rarely have allies remained so at odds on priorities. The US and Nato see no parallel between an organisation they consider a threat to the world order, with a clear intent to wreak havoc far and wide, and an ethnic group they are inclined to accept wants more autonomy, but not independence.

Turkey is having none of it. As it haggled with the US over access to its bases and airspace, the YPG moved farther into Syria, especially towards the Isis hub of Raqqa, and quietly consolidated its hold in the north-west. By late last summer, it became clear to Ankara that the Syrian Kurds had successfully used the chaos of war, and the backing of Turkey’s main western ally, to expand its border footprint.

The Kurds controlled a stretch from Irfin in the north-west to just west of Azaz. Only a gap of roughly 100 miles separated the next area of Kurdish influence, which then stretched all the way to the Iraqi border. The realisation led Ankara to renege on its ban on US jets. However, in return for allowing them to use Incirlik, it pressed for a safe haven within the 100-mile stretch, the purpose of which was to keep the Kurds away.

As Ankara sees things, its allies and its foes have now declared their hands. The US has little interest in reining in the YPG. The Kurds themselves have partnered with the Assad regime, after feigning ambivalence throughout the war, and Russia has partnered with the Kurds in western Syria, while the US partners with them in the east.

The YPG advances have been made possible by Russian air cover. After the Menagh air base was seized from opposition groups, among them jihadis, they moved across the north towards a 60-mile stretch of border in which they have never had a stronghold.

One western diplomat said: “What’s happening in Azaz is all down to the Russians. While they complain in the [UN] security council about Turkey, they do all they can to provoke things.”

Russia’s gamble is that Turkey’s bite does not match its bark. Ever since a Turkish jet shot down a Russian fighter in southern Turkey last November, both sides have faced off tensely. Russia is supporting Iran in Syria, where the Iranians are marshalling the ground forces aiming to besiege Aleppo.

The pro-Assad axis is ascendant for the first time in the war for the north, and there appears little that Turkey can now do to avoid the fall of Aleppo, apart from launching an extensive intervention of its own. So far, Turkey has confined its response to shelling YPG positions and warning the Kurds away from Azaz. It claims to have allowed roughly 900 Syrian rebel fighters to cross back into Syria from Turkey last week. However, western officials who monitor rebel movements have yet to confirm such a deployment. Also unconfirmed are claims by Saudi Arabia that it has already sent fighter jets to southern Turkey, ostensibly to join the air coalition against Isis. “There is a lot of talking going on,” the western official said. “Everyone is very agitated, but they remain in a bind.”

Saudi Arabia, too, has invested a lot in the anti-Assad opposition over the past three years. It has bankrolled a US training programme of some anti-Assad rebels and, more instructively, has supplied several thousand guided anti-tank missiles, which did serious damage to ageing Syrian troop carriers and tanks throughout 2015.

“They were the main reason that Russia intervened so forcefully,” said a senior Arab backer of the Syrian regime. “The Iranians went to Moscow and showed [Vladimir] Putin what was happening. He sent his bombers to Latakia within a week.”

Saudi and Turkish anger at the US remains palpable. “They have done nothing but enable Putin,” said a senior Saudi official in Riyadh this month. “Can this really be incompetence, or is there a strategy behind this to force their enemies to fight each other to the death in this part of the world? Do they really think they can walk away from their responsibilities like this?”

A change in the way the US projects its power in the Middle East is seen by its allies, particularly Saudi Arabia and the Gulf Cooperation Council, as a key driver of the conflict. In his final year as US president, Barack Obama has shown no appetite for trying to steward an outcome from one of the region’s most intractable conflicts. “He thinks he could never do anything about it,” the Saudi official said. “Well, you certainly can’t from the sidelines.”

Ankara, too, has grave misgivings about the US, which centre on what direct support for the YPG in the east and tacit backing for the Russian attacks in the west mean for longstanding alliances. The mistrust cuts both ways. The US remains convinced that Turkey has, at times throughout the war, dealt with Isis and has enabled its rise through a lax border regime early on, and a cross-border black market oil trade. While Turkey has joined the coalition against the terror organisation, the number of air attacks it launches against the PKK and YPG continues to dwarf those it launches against Isis.

With its air campaign in Syria now into a fifth month, Russia is also showing little interest in Isis, while continuing to batter opposition groups who have taken the fight to Assad. For now, Putin continues to enjoy the run of the war, manipulating the Kurds, needling the Turks and propping up Assad. If Azaz comes under genuine threat, however, that may change.

“The YPG should not delude themselves, said the Turkish prime minister, Ahmet Davutoglu, last week. “If they think they can defy us more, they truly are foolish.”

Who prevails in the narrow strip of land in northern Syria could well be determined in the coming weeks. “Much will depend on who is better at brinkmanship,” said the western official. “At the moment, it’s the Russians. But they play a high-risk hand.”

A Syrian boy in the devastated Sukari district in the northern city of Aleppo. Photograph: Baraa Al-Halabi/AFP/Getty Images

THE GREAT GAME: THE KEY PLAYERS AND WHAT THEY WANT



IRAN

Tehran, which is among President Bashar al-Assad’s powerful allies, is determined to secure an arc of influence extending to southern Lebanon and anchored in Damascus. It will continue to fund and direct the war and believes its military muscle is prevailing. Emboldened by its nuclear deal with the west, it sees little point in negotiating with weakened opposition and reluctant backers.

RUSSIA

Re-securing Syria in its orbit is very important to President Vladimir Putin’s resurgent aims for Russia. If it does so, it would start to eclipse the US as the pre-eminent regional power, unsettle a Nato frontline (in Turkey), establish a stronghold in the eastern Mediterranean and anchor Moscow’s hand with an ascendant Iran. Its immediate goal is to destroy the anti-Assad opposition, then look for partners to fight Isis. Putin wants to own the outcome.

UNITED STATES

Washington is determined to confine its role to fighting Isis. It is using the nuclear deal with Iran as a test of good faith in its broader role in the region. The US administration is not yet a full turn away from finding alliances in Riyadh and the Gulf, a sign of its sharply reduced projection and new foreign policy objectives after decades of prominent roles in regional wars. President Barack Obama is facing pointed criticism that the US has bowed to Russia.

ASSAD

President Assad was on the ropes before help arrived, losing large swaths of the country and in trouble in his heartland. He now aims to reassert control over all lost territory, which will be impossible without sustained and widespread help from Iran and Russia. His ambitions are curtailed by his dependence.

TURKEY

Ankara wants the Kurds as far away from the 800-mile border as possible. Deeply uncomfortable with US support for the YPG in the east and Russian backing for it in the west, it views the war against the insurgent PKK in Turkey and Kurdish advances in Syria through the same prism. Ankara is also bothered about the Russian bombing of the opposition forces it backs. Now it is weighing a response.

SAUDI ARABIA

Riyadh does not want to see the Syrian opposition lose – and especially not to see Iranian-backed pro-Assad groups win. The regime is increasingly bothered by Iran’s gains, but neutered by Russia’s entry into the Syrian war. It claims to have sent jets to Turkey, but hasn’t. Like Turkey, it is weighing a response, but it is very wary of how a war with Iran would ignite the region.

THE KURDS

Syria’s Kurds tried to sit out the early war years. They agreed with the US last year to act as a ground force in its air campaign against Isis, moving into parts of the north-west they had never controlled. Now, facilitated by Russia and Assad, the Kurds are making bold moves towards areas close to the Turkish border. The manoeuvres are either an attempt to stake a claim in whatever emerges from the ruins of the north, or to establish a foothold along the entire border for the first time.