Syrian government troops have moved into towns and villages in northern Syria, setting up a potential clash with Turkish-led forces advancing in the area.

The move came as long-standing alliances in the region begin to shift or crumble following the pullback of US forces.

The deployment near the Turkish border came after Syrian Kurdish forces previously allied with the US said they had reached a deal with President Bashar Assad’s government to help them fend off Turkey’s invasion, now in its sixth day.

Assad’s return to the region his troops abandoned in 2012 at the height of the Syrian civil war is a turning point in an eight-year civil war, giving another major boost to his government and its Russian backers and is like to endanger, if not altogether crush, the brief experiment in self-rule set up by Syria’s Kurds since the conflict began.

Residents welcome Syrian troops
Residents welcome Syrian troops (AP)

The fast-deteriorating situation was set in motion last week, when US President Donald Trump ordered American troops in northern Syria to step aside, clearing the way for an attack by Turkey, which regards the Kurdish fighters as terrorists.

Since 2014, the Kurds have fought alongside the US in defeating the so-called Islamic State group in Syria, and Mr Trump’s move was condemned at home and abroad as a betrayal of an ally.

In the past five days, Turkish troops and their allies have pushed into northern towns and villages, clashing with the Kurdish fighters over a stretch of 125 miles. The offensive has displaced at least 130,000 people.

Abandoned in the middle of the battlefield, the Kurds turned to Assad and Russia for protection and announced on Sunday night that Syrian government troops would be deployed in Kurdish-controlled towns and villages along the border to help repel Turkish advances.

A Turkish tank is driven into position
A Turkish tank is driven into position (Emrah Gurel/AP)

Kurdish official Aldar Khalil said in a statement that the aim of the agreement is for Syrian troops to be deployed along the border, except for the area between the towns of Ras al-Ayn and Tal Abyad, where Turkish troops are advancing.

He added that the autonomous authority will continue to run daily affairs in north-east Syria.

Syrian state media broadcast repeated footage of government forces entering northern towns and villages with residents chanting slogans in support of Assad, while others rushed to hug the soldiers.

Syrian fighters backed by Turkey said they began an offensive alongside Turkish troops to capture the Kurdish-held town of Manbij, on the western flank of the Euphrates. Mustafa Sejari, an official with the Turkey-backed fighters, tweeted: “The battle of Manbij has begun.”

Turkey’s private NTV television reported that Turkish special forces and commandos began advancing toward Manbij in the afternoon. CNN-Turk also mentioned the attack.

Recep Tayyip Erdogan
Recep Tayyip Erdogan (Presidential Press Service/AP

Turkish President Recep Tayyip Erdogan signalled earlier in the day that his military was ready to begin the assault on Manbij, with a goal of returning the city to Arab populations who he said were its rightful owners.

Mr Erdogan said Turkey’s military offensive into north-east Syria is as “vital” to Ankara as its 1974 military intervention in Cyprus, which split the island. He also made clear Turkey would not halt its offensive despite the widespread condemnation.

Turkey justified its invasion to the United Nations by saying it is exercising its right to self-defence under the UN Charter, according to a letter circulated on Monday.

Ankara said the military offensive was undertaken to counter an “imminent terrorist threat” and to ensure the security of its borders from Syrian Kurdish militias, whom it calls terrorists, and IS.

The military action sets up a potential clash between Turkey and Syria and raises the spectre of a resurgent IS group as the US relinquishes any remaining influence in northern Syria to Assad and Russia.

European Union nations condemned Turkey’s military offensive and joined France and Germany in banning arms sales to Ankara, a rare move against a Nato ally for many of them.

Many EU foreign ministers were looking beyond a strong statement condemning the military operation that has destabilised the region and wanted to make sure their move would carry some sting.

They also prepared sanctions against Turkish companies and individuals involved in gas drilling in east Mediterranean waters where EU member Cyprus has exclusive economic rights and has licensed European energy companies to carry out a hydrocarbons search.

The sanctions, which Cypriot officials said may include an asset freeze, travel bans and a sales ban on material used in drilling, could be implemented at short notice.