Ankara stepped up its assault on Kurdish-held border towns in northeastern Syria on Saturday, defying mounting threats of international sanctions, even from Washington.

Buoyed by a night of steady advances in the countryside, Turkish troops and their Syrian allies entered the battleground town of Ras Al Ain, sources on both sides said.

The Turkish defence ministry hailed its forces’ capture of the first Kurdish-held town of the offensive so far.

But Ras Al Ain’s Kurdish defenders denied the town had fallen and a correspondent near the town said Turkish troops and their Syrian allies had entered but had yet to capture it.

The Kurdish-led Syrian Democratic Forces, who were the main ground partner in the US-led campaign against the Daesh group, called on the United States to assume its “moral obligations” and protect them.

US President Donald Trump has faced a firestorm of criticism, even from his own domestic supporters, for abandoning a loyal ally and stands accused of giving Turkey a green light to launch the offensive after ordering American troops to pull back from the border.

The SDF have taken mounting losses against the vastly superior firepower of the Turkish army.

At least 23 SDF fighters have been killed, including in overnight clashes, bringing the over death toll since the Turkish offensive began on Wednesday to 81, said the Syrian Observatory for Human Rights monitor.

Turkish air strikes on Kurdish-held towns and intense artillery exchanges caused mounting casualties on both sides of the border.

On the Syrian side at least 28 civilians have been killed, according to the Britain-based Observatory, and 17 are dead in Turkey, according to Turkish reports.

Four Turkish soldiers have been killed, Turkey’s defence ministry and state-run Anadolu news agency said.

The towns of Ras Al Ain and Tal Abyad further west have been primary goals of the Turkish offensive and have both come under heavy bombardment.

They lie at either end of a section of the border which although Kurdish-controlled has an ethnic Arab majority.

Ankara says its forces’ mission is to establish a safe zone run by its mainly Arab Syrian allies in which some of the 3.6 million mostly Arab refugees from Syria can be rehoused.

But the Kurds say the Turkish invasion amounts to an attempt to redraw the ethnic map of the region at their expense.

The operation has so far displaced some 100,000 people, according to the United Nations.

Roads leading out of the area have been filled with fleeing civilians, some on foot, other in vehicles piled high with their belongings.

“We always get displaced no matter where we go,” Yusra Al Saleh, 38, who fled violence along Syria’s northern border, said.

“We are destroyed.”

The Kurdish Red Crescent said it would no longer dispatch medical teams to Ras Al Ain because its ambulances are being hit by Turkish fire.

It said one of its medical points south of Ras Al Ain was hit by Turkish fire on Saturday, wounding an ambulance driver and damaging the vehicle.

Aid groups have warned of yet another humanitarian disaster in Syria’s eight-year-old war if the offensive is not stopped.

“More people are leaving on a daily base and those numbers will go up,” the World Food Programme (WFP) said.

Most of those fleeing were heading east towards the city of Hasakeh, which has not been targeted by Turkey.

“Turkey’s aim is to prevent further fleeing Syrian civilians from entering Turkey rather than genuinely providing protection,” Human Rights Watch.

The SDF lost 11,000 fighters in the protracted US-led campaign against Daesh before finally overrunning the militants’ self-proclaimed “caliphate” in March.

On Saturday, decried being “abandoned” by Washington.

“Our allies had guaranteed us protection ... but suddenly and without warning they abandoned us in an unjust decisions to withdraw their troops from the Turkish border,” a statement said.

Agence France-Presse