BEIRUT — A Kurdish-led force fighting the Islamic State group with the support of U.S. troops will close in on the extremists’ de facto capital Raqqa within a few weeks, but the battle for the city will be difficult, a U.S. military official said Thursday.

Air Force Col. John Dorrian said the U.S. force consisting of a couple of hundred Marines that arrived in the region south of the Syrian-Turkish border on Wednesday will not have any front-line roles but will provide artillery fire to support the advance of the Kurdish-led Syrian Democratic Forces.

“The intent of their presence is to provide all-weather fire support, artillery fire to support their advance as they continue the isolation of Raqqa,” he said. “This is just some added firepower that will be very difficult for the enemy to deal with.”

The deployment reflects Washington’s deeper involvement in Syria under the administration of President Trump and thrusts the U.S. further into a difficult diplomatic entanglement.

Dorrian told The Associated Press by telephone that the U.S.-backed force will close in on Raqqa within a few weeks and warned that the battle for the city will likely be difficult as the extremists are well entrenched. He said a complicating factor is that the U.S. does not have a partner government to work with in Syria as is the case in Iraq.

The U.S. already had some 500 advisers working with the Syrian Democratic Forces in addition to a force of 400 that arrived more recently, Dorrian said. He said the troops include U.S. Army Rangers already in Syria.

The SDF, a coalition of Kurdish, Arab and Christian fighters, has been the most effective force fighting the Islamic State group in Syria. The SDF has been on the offensive in the Raqqa area since November under the cover of airstrikes by the U.S.-led coalition with the aim of eventually besieging the city before storming it.

Dorrian said the SDF “made excellent progress and the enemy hasn’t been able to stop them from doing the things that they set out to do.” He added that SDF fighters have so far captured about 2,471 square miles of terrain from the radical militants.

“That’s excellent progress,” Dorrian said, adding that SDF fighters have also cut many supply lines used by ISIS to try to either escape from the city “or to have fighters leave the area and conduct terrorist operations elsewhere away from Iraq and Syria.”

Dorrian said the SDF will need a “few more weeks” to completely isolate Raqqa and a decision will be made about the timing “of the liberation battle to begin.”