The threat of a growing security vacuum in Syria as a result of Donald Trump’s decision to withdraw US troops has been underlined by an attack on a joint US-Kurdish patrol, which reportedly killed five people and injured at least two American soldiers.

The attack on Monday, in which a suicide bomber drove a car into a checkpoint, emphasised the vulnerability of American troops since the US president declared he was withdrawing 2,000 soldiers from northern Syria on the grounds that Islamic State has been defeated.

The bomber targeted a joint patrol by US forces and the Kurdish-dominated Syrian Democratic Forces (SDF) in the Hasakah countryside of north-east Syria.

Kurdish forces later claimed none of their number had been killed.

Recep Tayyip Erdoğan, the Turkish president, is threatening to send troops into US-overseen areas on the Syrian border.

He said preparations for a Turkish incursion into Syria were complete, but insisted the aim was not to undermine the territorial integrity of the country.

Erdoğan said: “We will deliver Manbij to its real owners. We don’t have eyes on anybody’s land. Those who insistently want to keep us away from these regions are seeking to strengthen terror organisations.”

The idea of a safe zone was promoted initially by Trump, but Erdoğan appears to sense the concept could become a joint Turkish-US plan in which the US could provide air cover and Turkey the ground troops.

Erdoğan said his warning that he would not allow the safe zone to become a swamp for Kurdish terrorists stemmed from Turkish experience of safe zones for Kurds in Northern Iraq.

The attack on the convoy took place two days after Trump attended a ceremony marking the return of the bodies of four US citizens, including two soldiers killed on 16 January by an Isis suicide bomber in the SDF-held town of Manbij.

That attack was the deadliest on US troops since they were deployed to Syria in 2014 to assist local forces against Isis.

Overruling his security apparatus, Trump announced in December that 2,000 elite US troops would withdraw from Syria, which led to the resignations of his defence secretary, Jim Mattis, and Brett McGurk, the special envoy to the coalition fighting Isis.

The latest attack on a US convoy will put pressure on Trump either to accelerate the withdrawal or set out how he intends to protect American forces before they leave.

In a TV interview on Sunday, McGurk said Trump had no plan for Syria, and insisted that since Isis had not been defeated, Trump’s decision represented a threat to the west’s security.

He warned that Trump’s decision had endangered US troops, saying: “You never telegraph a punch when you’re in a military campaign. You also don’t telegraph your retreat.

“The minute you announce to the world that you’re leaving, a vacuum opens up and all the other powers in the region start making different calculations.”

Late on Sunday, Trump spoke to Erdoğan, who told him Turkish forces were ready to go into northern Syria, including Manbij, to fill the vacuum likely to be left by the US’s departure.

Speaking to Turkish businessmen on Monday, Erdoğan said he would set up a safety zone on the border between Syria and Turkey, largely by putting Turkish troops in charge of a 20-mile (32km) zone running the length of the border.

“We will never allow a safe zone in Syria transformed into another swamp against our country,” he said, adding that he would hand over Manbij to its rightful owners. He also insisted Turkey could remove terrorists from the area with US logistical support.

The Kurdish People’s Protection Units (YPG) have carried out the bulk of the fighting in the past four years on behalf of the US against Isis in Syria.

They believe Erdoğan will use the safe zone concept as a way of attacking YPG forces, and any decision by the US to provide logistical support to Turkey to seize the area would be regarded as a further betrayal.

Erdoğan regards the YPG as inextricably linked with the Kurdistan Workers’ party (PKK), which is fighting for greater independence inside Turkey.

Turkey’s president sees the YPG and PKK as a single terrorist force that represents an existential threat to the Turkish state.

The UK, which along with France has special forces operating in the area, was effectively given no warning of Trump’s decision. Since the announcement, US officials have given different accounts of the pace of the withdrawal and the plan for what will replace US forces.

The Kurds, feeling deserted by the US, are increasingly inclined to reach an accommodation in a federal Syria with the president, Bashar al-Assad, rather than accept Turkish rule. Turkey has led the opposition to Assad.

Erdoğan will meet Vladimir Putin, the Russian president, later this month to discuss whether they can reach a political agreement on Syria’s future, including the enclave of Idlib, still held by groups opposed to Assad.

Mevlüt Çavuşoğlu, the Turkish foreign minister, will fly to Washington for a meeting of the US-led coalition against Isis on 6 February.

By then, allies in the global coalition will be impatient for the US to have prepared a coherent strategy to resist the re-emergence of Isis in Syria and fill the political void left by the US’s departure.