Turkish President Tayyip Erdogan has met with U.S. Republican Senator Lindsey Graham to discuss the situation in Syria as the United States prepares to withdraw troops.

Graham, a prominent voice on foreign affairs in the U.S., met with Erdogan and other Turkish officials Friday for talks that were also expected to include a proposal for the creation of a "safe zone" in northeast Syria.

The visit comes days after a suicide bombing, claimed by the Islamic State of Iraq and Syria (ISIS), killed two U.S. service members and two American civilians in the northeast town of Manbij. It was the deadliest attack on U.S. forces in the country since they went in to fight ISIS in 2015.

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Graham has said he's concerned that U.S. President Donald Trump's announcement that American forces are leaving the country has emboldened ISIS militants, and created dangerous uncertainty for American allies.

Turkish President Recep Tayyip Erdogan (R) shakes hands with U.S. Senator Lindsey Graham as they pose for a photo at Presidential Complex in Ankara, Turkey, Jan. 18, 2019. Getty

Mr. Trump declared ISIS defeated in mid-December, and Vice President Mike Pence repeated the assertion on Wednesday, just after the Pentagon confirmed that four Americans had died in the attack blamed on the group. As CBS News correspondent Charlie D'Agata saw first-hand this week in eastern Syria, America's fight against ISIS in Syria is not over, and ISIS, if anything, is morphing into an entrenched insurgency with the ability to strike all over the country.

Those same concerns were voiced on Friday in a damning article in the Washington Post by the former senior U.S. envoy to the region, Brett McGurk.

McGurk resigned from his post soon after President Trump declared ISIS defeated and said he would bring America's forces home. In his Post column, he slams the president's decision to withdrawal U.S. troops and says if Mr. Trump does not reverse it, "Our partners will stop listening and make decisions that run contrary to our interests. Our adversaries will play for time, knowing the United States is on its way out. The Islamic State and other extremist groups will fill the void opened by our departure, regenerating their capacity to threaten our friends in Europe — as they did throughout 2016 — and ultimately our own homeland."

"The irony is that defeating the Islamic State is what the president said from the beginning was his goal," wrote McGurk. "In 2016, he vowed to 'knock the hell out of ISIS.' His recent choices, unfortunately, are already giving the Islamic State — and other American adversaries — new life."