Top Republicans pointed to an ISIS-claimed attack in Syria on Wednesday as a sign President Trump should not move forward with his plan to withdraw US troops from the country.

"My concern by the statements made by President Trump is that you have set in motion enthusiasm by the enemy we're fighting," Sen. Lindsey Graham said.

Meanwhile, Sen. Marco Rubio warned about the consequences of "retreat."

The deaths of the four Americans on Wednesday, including two US soldiers, were a result of a suicide bombing in Manbij, Syria.

Top Republicans on Wednesday warned President Trump against embracing "retreat" in Syria after an ISIS-claimed attack killed two US soldiers and two other Americans, pointing to the deadly attack as yet another sign the president should back down on his plan to withdraw troops from the war-torn country.

Republican Sen. Lindsey Graham, a key Trump ally who serves on the Senate Foreign Relations Committee, suggested Trump's Syria pullout had bolstered ISIS' resolve.

"My concern by the statements made by President Trump is that you have set in motion enthusiasm by the enemy we're fighting," Graham said in impromptu remarks as he chaired a Senate Judiciary Committee hearing.

Read more: US troops die in suicide bombing claimed by ISIS, calling into question Trump's declaration of victory

Graham made it clear he hopes Trump will take a careful look at his policy toward Syria following Wednesday's attack.

"You make people we're trying to help wonder about us. As they get bolder, the people we're trying to help become more uncertain. I saw this in Iraq. And I’m now seeing it in Syria," Graham said in an apparent reference to the rise of ISIS in the years that followed the withdrawal of US troops from Iraq in 2011.

Graham said he understood people's frustrations at the ongoing presence of US troops in Syria, and that "every American" wants them to "come home." But he suggested that keeping troops in Syria is a matter of ensuring America's safety.

"We’re never going to be safe here unless we're willing to help people over there who will stand against this radical ideology," Graham said.

"To those who lost their lives today in Syria, you were defending America, in my view," the South Carolina senator added. "To those in Syria who are trying to work together, you're providing the best and only hope to your country. I hope the president will look long and hard about what we're doing in Syria."

Republican Sen. Marco Rubio, who also sits on the Senate Foreign Relations Committee, echoed Graham's sentiments.

"[ISIS] has claimed credit for killing American troops in [Syria] today," Rubio tweeted on Wednesday. "If true, it is a tragic reminder that ISIS not been defeated and is transforming into a dangerous insurgency. This is no time to retreat from the fight against ISIS. Will only embolden & strengthen them."

Meanwhile, GOP Rep. Adam Kinzinger, a US Air Force veterean who served in Iraq and Afghanistan, also warned of the dangers of "retreating" in Syria.

"Retreating from a fight against ISIS is only gonna send the wrong message and frankly, pour fuel on the recruiting efforts of ISIS," Kinzinger told CNN on Wednesday.

The deaths of the four Americans on Wednesday were a result of an explosion in Manbij, Syria. Three other troops were also injured in the incident.

"U.S. service members were killed during an explosion while conducting a routine patrol in Syria today. We are still gathering information and will share additional details at a later time," Operation Inherent Resolve tweeted Wednesday.

In a statement on the incident that made no mention of ISIS, the White House on Wednesday said, "Our deepest sympathies and love go out to the families of the brave American heroes who were killed today in Syria. We also pray for the soldiers who were wounded in the attack. Our service members and their families have all sacrificed so much for our country."

Read more: Pence repeated the claim that ISIS is 'defeated' just hours after US troops died in a devastating ISIS-claimed attack in Syria

Wednesday's lethal attack came exactly four weeks after Trump tweeted, "We have defeated ISIS in Syria." This came as Trump abruptly announced a plan to withdraw the roughly 2,000 troops stationed in Syria, prompting alarm in Washington due to the ongoing, well-documented presence of ISIS in the region.

In the days that followed, Trump flip-flopped on his claim ISIS is defeated as he scrambled to justify the controversial, hasty plan.

The president has faced criticism from the military and politicians on both sides of the aisle over the pullout and the opacity surrounding it. Former Defense Secretary James Mattis resigned a day after Trump made the announcement. Mattis had disagreed with Trump on an array of issues, but the Syria pullout seemed to be the final straw.

The White House has offered little in the way of specifics about the pullout which has led to confusion in the Pentagon and beyond. No US troops have been pulled out of Syria yet, but the military has started withdrawing equipment.