The Thursday attack occurred during an operation against the Islamic State that also left a British service member dead. Five others were injured.
The deaths occurred about two hours after Trump promised in a speech in Ohio to withdraw the roughly 2,000 U.S. troops in Syria “very soon” and “let the other people take care of it.”
The incident, which took place in the city of Manbij in northern Syria, is under investigation, the Defense Department said.
Dunbar joined the Army in 2005 and was deployed to both Afghanistan and Iraq. He was assigned to the headquarters of U.S. Army Special Operations Command at Fort Bragg, N.C., in 2013. He earned three Bronze Star Medals.
Also killed was Sgt. Matt Tonroe, a British soldier who served in the 3rd Battalion of the elite Parachute Regiment. Tonroe had deployed numerous times for operations in Afghanistan and the Middle East.
Trump has been pressing for the removal of U.S. troops from Syria, saying it makes little sense for the United States to have so many forces in the country if it has all but won the war against the Islamic State. His remarks were not planned, and it was not clear what prompted him to mention Syria in a speech about infrastructure. One administration official said it could be a year or longer before such a move happens.
The president’s advisers have persuaded him to stay for now to prevent the Islamic State from reemerging and to lay the groundwork for a potential peace agreement that would be beneficial to the United States.