The four Americans killed Wednesday in an explosion in Syria were a soldier, a sailor, a civilian member of the Department of Defense and a contractor supporting the department, NBC News reported.
Three have been publicly identified: Army Chief Warrant Officer Jonathan R. Farmer, 37; Navy Chief Cryptologic Technician Shannon M. Kent, 35, and Scott A. Wirtz. The contractor has not been identified.
The deaths of two U.S. service members made Wednesday the deadliest day for Americans in Syria.
ISIS claimed responsibility for the attack, claiming it was a suicide bombing, though it did not immediately produce evidence to support the claim. American defense officials said that ISIS has not been present in the city for months and cautioned the group sometimes falsely claims credit for attacks.