A car bomb has targeted a joint convoy of US and allied Kurdish forces in northeastern Syria, marking the second attack against US forces in less than a week.

There were no casualties in Monday's attack in al-Shaddadi, a town in Hasakah governorate, according to US military Colonel Sean Ryan.

"We can confirm a combined US and Syrian partner force convoy was involved," said Ryan. "We will continue to review the situation and provide updates as appropriate."

The Kurdish Hawar news agency, based in northern Syria, said Monday's blast targeted a Syrian Kurdish checkpoint as a coalition convoy was passing near Al-Shaddadi. It said two Kurdish fighters were lightly wounded in the blast.

The incident came days after a suicide attack killed 16 people - including two US service members and two American civilians - in the northern Syrian town of Manbij.

A website linked to the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) said the group claimed responsibility for both attacks.

US President Donald Trump claimed ISIL has been defeated in Syria which was his stated reason for pulling 2,000 US troops out of the country.

ISIL has been driven out of virtually all the territory it once held in Syria and Iraq but continues to carry out sporadic attacks in both countries.

Trump's withdrawal announcement last month surprised many politicians in Washington as well as Western and Kurdish allies fighting ISIL alongside the US.

Brett McGurk, presidential envoy to the US-led global coalition against ISIL, said the US has "no plan for Syria" as it proceeds with carrying out Trump's order.

'Safe zone'

The ISIL-claimed attacks took place in the highly strategic northeastern region.

Manbij is the main town on the westernmost edge of Syrian territory held by the US-backed Syrian Kurds, running along the border with Turkey.

Mixed Kurdish-Arab Syrian forces - known as the Syrian Democratic Forces (SDF) - liberated Manbij from ISIL in 2016 with help from the US-led coalition. But Kurdish control of the town infuriated Turkey, which views the main US Kurdish ally, the People's Protection Units or YPG, as "terrorists" linked to Kurdish fighters on its own soil.

The town has been at the centre of tensions in northern Syria, with militaries of two NATO members, the US and Turkey, on opposing sides.

Also on Monday, Turkish President Recep Tayyip Erdogan said his country would not allow a "safe zone" it is considering setting up in northern Syria to become a base for Kurdish separatists.

Last week, Erdogan said he and Trump had discussed Turkey setting up a 32km-deep safe zone inside Syria along the length of the border between the two countries.

Erdogan said Turkey would work with anyone willing to provide it logistical support for the zone, but that it would take action in Syria if promises were not kept.

"We will never allow a safe zone that will turn into a new swamp for Turkey like the one in northern Iraq, where we still experience problems," said Erdogan.

"We are not talking of a safe zone [as protection] against Turkey, but rather one against terrorists."