Footage of a Turkey-backed militia threatening to execute any Kurds they find in Northern Syria has emerged, as both sides accused each other of breaking a ceasefire agreement negotiated by the United States.

The return of violence comes as President Recep Erdogan, who agreed to a five-day truce in his military offensive with US Vice President Mike Pence, vowed to 'crush the heads' of Kurdish forces if they do not retreat from a 120-kilometre stretch of the border.

Turkey's offensive, launched earlier this month, has prompted hundreds of thousands to flee their homes - the latest humanitarian crisis of Syria's eight-year civil war.

Earlier today a Turkish soldier was killed and another wounded in an attack by Syrian Kurdish forces near the Tal Abiad border town by what the Turkish defence ministry called 'terrorists'.

'One of our heroic comrades fell martyr and another was wounded after anti-tank and small arms fire by... terrorists during their reconnaissance and surveillance mission,' the ministry said in a statement.

American volunteers search the rubble of a house for the bodies of victims in the border town of Ras al-Ayn, northeastern Syria. Fighting in the area has continued while the US ceasefire collapsed

Turkey's offensive, launched earlier this month, has prompted hundreds of thousands to flee their homes - the latest humanitarian crisis of Syria's eight-year civil war

The army returned fire in self-defence, it added.

Further east along the Syria-Turkey border, a militia group in the town of Ras al-Ayn posted a disturbing video in which they proudly claimed they would display the heads of any Kurdish 'infidel' they find.

In the footage, one of the group shouts: 'Desist sons of Muwali. We've come to behead you, you infidels, you apostates. God willing, we're coming for you.'

Another adds: 'Just a few hours and we'll show you the (decapitated) heads.'

A third then quips: 'Victory only comes from God! With beheading.'

Another, more graphic video was also posted, showing summary executions believed to be on the M4 highway, an east-west road further inside Syria.

The head spokesman for the Syrian Democratic Forces posted the footage, saying: 'Turkish-backed armed groups threaten to behead any "infidel Kurd" they capture on their way to NE Syria.

A militia group in the town of Ras al-Ayn posted a disturbing video in which they proudly claimed they would display the heads of any Kurdish 'infidel' they find

In the footage, one of the group shouts: 'Desist sons of Muwali. We've come to behead you, you infidels, you apostates. God willing, we're coming for you'

Another adds: 'Just a few hours and we'll show you the (decapitated) heads'

'To all those who are worried that ISIS may come back. ISIS is already back to NE Syria with Turkish protection.'

Yesterday SDF commander Abdi accused Turkey of sabotaging the truce by blocking the withdrawal of his forces from flashpoint border town Ras al-Ain.

The Turkish defence ministry said Sunday that Kurdish forces carried out 20 attacks.

'Despite all the hostile acts in violation of the agreement, a convoy of 39 vehicles, mostly ambulances, safely entered and exited Ras al-Ain on Saturday' to help evacuate the wounded, the ministry said.

Turkish presidency spokesman Ibrahim Kalin said Ankara abided by the agreement and urged the US to use its leverage to ensure Syrian Kurdish forces' pullout.

'We are committed to this agreement: Within five days they are supposed to leave and we have told our American colleagues to use their leverage, their connections to make sure that they leave without any incidents,' he said in Istanbul yesterday.

Syrians flee with their belongings the countryside of the northeastern Syrian town of Ras al-Ain on the Turkish border, toward the west to the town of Tal Tamr

The return of violence comes as President Recep Erdogan (left), who agreed to a five-day truce in his military offensive with US Vice President Mike Pence (right), vowed to 'crush the heads' of Kurdish forces if they do not retreat from a 120-kilometre stretch of the border

The Turkish offensive launched earlier this month has prompted hundreds of thousands to flee their homes in the latest humanitarian crisis of Syria's eight-year civil war.

Syrian Democratic Forces are now asking the United States to pressure Turkey to allow the safe passage of civilians out of the 120-kilometre-long area of border.

Yesterday a senior Syrian Kurdish official said his forces would pull back from a border area in accordance with the US brokered deal when Turkey allows the evacuation of its remaining fighters and civilians from a besieged town there.

Redur Khalil, a senior Syrian Democratic Forces official, said the plan for evacuation from the town of Ras al-Ayn is set for today, if there were no delays.

The Kurdish Forces announced they would move 30km back in to the safe zone yesterday and today after Turkish President Erdogan agreed a ceasefire with the United States to allow civilians and soldiers to withdraw

People comfort a wounded man after an activated mine exploded in a house set up by Kurdish group the PKK, listed as a terrorist organization by Turkey

Earlier today a Turkish soldier was killed and another wounded in an attack by Syrian Kurdish forces near the Tal Abiad border town

This is the first time the Kurdish force has publicly acknowledged it will withdraw from the border, saying it has coordinated it with the Americans. Medical staff treats a wounded man in an ambulance following the explosion

He says only after that will his forces pull back from the area between the towns of Ras al-Ayn and Tal-Aybad. It will withdraw and move back from the border 30 kilometres.

This is the first time the Kurdish force has publicly acknowledged it will withdraw from the border, saying it has coordinated it with the Americans. The agreement has not specified the area of its pullback.

Previous agreements between the US and Turkey over a 'safe zone' along the Syria-Turkish border floundered over the diverging definitions of the area.

Khalil said a partial evacuation happened earlier Saturday from Ras al-Ayn after much stalling and with U.S. coordination.