Senator Lindsey Graham said on Saturday he hoped Donald Trump would slow the US withdrawal from Syria until Islamic State is destroyed, warning that if not thought through, the pullout can create an “Iraq on steroids”.

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A bomb attack in Manbij this week, claimed by the militant group, killed two US troops and two civilians working for the US military in northern Syria, along with other civilians.

Trump was due to attend the repatriation of the bodies at Dover air base in Delaware. The president told reporters his Syria policy had made progress but that some work remained in destroying Isis targets. He defended his plans for a withdrawal.

“It’s moving along very well, but when I took over it was a total mess,” he said. “But you do have to ask yourself, we’re killing Isis for Russia, for Iran, for Syria, for Iraq, for a lot of other places. At some point you want to bring our people back home.”

Army chief warrant officer Jonathan Farmer, 37, of Boynton Beach, Florida; navy chief cryptologic technician Shannon Kent, 35, identified as being from upstate New York; and Scott Wirtz, a civilian Department of Defense employee from St Louis, died in the Manbij attack, the Pentagon said in a statement. It did not identify the fourth person killed, a contractor working for a private company.

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Graham, from South Carolina, is a friend and ally of the president who regularly claims to have his ear. Speaking in Ankara, he also said he believed the chair of the joint chiefs of staff, Joseph Dunford, was working on a plan with Turkey to move Kurdish fighters away from the Turkish border.

Trump announced last month that Isis had been defeated in Syria and he would pull US forces out of the country. The decision injected new uncertainty into the eight-year Syrian war and spurred a flurry of contacts over how a resulting security vacuum will be filled across northern and eastern Syria.

The withdrawal of US troops from Iraq by the end of 2011, nine years after the 2003 US-led invasion, left space for the rise of Isis militants, prompting the US to intervene again.

The attack in Manbij appeared to be the deadliest on US forces in Syria since they deployed on the ground there in 2015. The town is controlled by a militia allied to US-backed Kurdish forces.

It remains unclear when US forces will leave northern Syria, where both Turkey and the Syrian government of Bashar al-Assad are ready to fill the vacuum. The YPG militia allied to the fighters holding Manbij last month invited Assad into the area around the town to forestall a potential Turkish assault.

The Turkish president, Recep Tayyip Erdoğan, said last week he had discussed a safe zone with Trump, which Turkey would set up inside Syria along their border.

“Here’s the good news,” said Graham. “Gen Dunford, I think, has a plan that he’s working on with the Turkish military that can accomplish these objectives and they are to move the YPG elements away from Turkey.”

He also said heavy armaments should be taken from the Kurdish groups. Turkey says the YPG is a terrorist organisation and an extension of the outlawed Kurdistan Workers party (PKK). Graham also said the political arm of the YPG was interlinked and interconnected with the PKK, which has waged a decades-long insurgency on Turkish soil.

“A withdrawal that does not outline the points I have made will not end the war against Isis, it will start a new war,” he said. “This war will be a necessity by Turkey, to go into Syria and clear out armed elements that Turkey believes poses a threat to its sovereignty.”

A Turkish official told Reuters the US should consider Turkey’s priorities, not those of the YPG.

“After [Graham’s] meetings in Turkey, Erdoğan and other officials, we hope the US will understand more the situation,” the official said.