The troops are not in a direct combat role but are calling in air strikes and are working closer to the fight than did US forces supporting the Iraqi military in Mosul.
Official: US troops have entered Raqqa
American military advisors are operating inside the city of Raqqa,ISIL's last major stronghold in Syria, a US official said on Wednesday.
The troops, many of them special operations forces, are working in an "advise, assist and accompany" role to support local fighters from the Syrian Democratic Forces as they battle ISIL, said Colonel Ryan Dillon, a military spokesman.
The troops are not in a direct combat role but are calling in air strikes and are working closer to the fight than was the case with US forces supporting the Iraqi military in Mosul.
"They are much more exposed to enemy contact than those in Iraq," Col Dillon said. But their numbers in Raqqa did not run into hundreds, he added.
The operation to capture Raqqa began in November and on June 6 the SDF entered the city. With help from the US-led coalition, the SDF this month breeched an ancient wall by Raqqa's Old City, where diehard militants are making a last stand.
Col Dillon said the coalition had seen ISIL increasingly using commercial drones that have been rigged with explosives. They employed a similar tactic in Mosul.
"Over the course over the last week or two, it has increased as we've continued to push in closer inside of Raqqa city center," he said.
The US military is secretive about exactly how big its presence is in Syria, but has previously said about 500 special operations fighters are there to train and assist the SDF, an Arab-Kurdish alliance.
Additionally, US Marines are operating an artillery battery to help in the Raqqa offensive.