This picture taken on Monday shows smoke rises from the Syrian town of Ras al-Ain, from the Turkish side of the border at Ceylanpinar district in Sanliurfa, on the sixth day of Turkey's military operation against Kurdish forces. Photo: AFP

Deadly Turkish air strikes Friday shattered an hours-old US-brokered deal to stop Ankara's military offensive against Kurdish forces in northeastern Syria.

The cease-fire announced late Thursday was meant to provide a pause for the evacuation of Kurdish fighters from the battleground border town of Ras al-Ain and other areas Turkey wants to control along its border with Syria.

The five-day suspension looked designed to help Turkey achieve its main territorial goals without fighting but its Syrian proxies continued to clash with Kurdish fighters Friday and an air strike killed five civilians.

"Five civilians were killed in Turkish air strikes on the village of Bab al-Kheir, east of Ras al-Ain," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said.

The Britain-based war monitor said four fighters of the Syrian Democratic Forces - the de facto army of the embattled Kurdish autonomous region - were killed in the strike.

The incident took place even as a 200-vehicle convoy headed towards Ras al-Ain to evacuate civilians who have been virtually besieged there since the start of Turkey's cross-border assault on October 9.

Mustefa Bali, a spokesman for the SDF, said Turkey was clearly violating the terms of the agreement reached during a Thursday visit to Ankara by US Vice President Mike Pence.

"Despite the agreement to halt the fighting, air and artillery attacks continue to target the positions of fighters, civilian settlements and the hospital" in Ras al-Ain, he said.

Under the deal, Kurdish forces are required to withdraw from a border strip 32 kilometers deep, clearing the way for a "safe zone" sought by Turkey.

The Kurdish-led Syrian Democratic Forces (SDF) had said they were ready to abide by the ceasefire in border territory between Ras al-Ain and Tal Abyad to its west.

The Turkish offensive was sparked by US President Donald Trump's announcement of an American withdrawal from northern Syria, leading critics to accuse him of betraying Washington's Kurdish allies.

On Thursday evening, Trump said he allowed the two sides to fight for a few days before brokering a truce as they were like "kids in a lot."

The Turkish military and its Syrian proxies have so far seized around 120 kilometers of territory along the border. More than 500 people have been killed on the two sides, including nearly 100 civilians, while around 300,000 have been displaced, according to the Observatory.