A suicide car bomb attack has killed five members of a Kurdish-led force while they were out on a patrol with US troops in northeastern Syria.

The five fighters from the Syrian Democratic Forces (SDF) were killed in the attack, which occurred near a checkpoint on a road near the town of al-Shadadi in Hasakah province, according to UK-based war monitor Syrian Observatory for Human Rights.

"A combined US and Syrian partner force convoy was involved in an apparent VBIED attack today in Syria," Sean Ryan, spokesman for the US-led coalition, wrote on Twitter, adding that there were no US casualties.

The incident marked the third major attack on SDF and coalition forces since Donald Trump, the US president, announced he was withdrawing all 2,000 troops from Syria in December.

Last week a suicide bomber detonated an explosive vest outside a restaurant in northern city of Manbij, where US coalition forces were on patrol, killing 16 people including two American soldiers and two American contractors. Three more US servicemen were injured.

The attack, which was claimed by Islamic State of Iraq and the Levant (Isil), was the deadliest against US forces since they deployed in Syria in 2015.

On January 5, they fired a heat-seeking missile into a group of coalition troops on patrol further south in Deir Ezzor, injuring five British special forces.