The soldier was killed by an improvised explosive device near Ayn Issa, according to a statement by U.S. Central Command (CENTCOM). Ayn Issa is about an hour from Raqqa, Daesh's self-declared capital in Syria.
Fox News reports that the soldier, whose name has not been released, was embedded with the Kurdish-led Syrian Democratic Forces, one of roughly 300 American service members embedded with the group.
US Defense Secretary Ash Carter called the death a "painful reminder of the dangers our men and women in uniform face around the world to keep us safe" in a statement of condolence on the death, the first declared US casualty in the country.
US Special Forces soldiers have been deployed in Syria since October 2015.
"The entire counter-ISIL Coalition sends our condolences to this hero's family, friends and teammates," Lieutenant General Stephen Townsend, commander of Combined Joint Task Force — Operation Inherent Resolve, said in a statement. "On this Thanksgiving, please be thankful that there are service members willing to take up the fight to protect our homeland from [Daesh's] hateful and brutal ideology."