Speaking to CNN, Rubio described the death as a mishap that occurred during operations against an Iranian unmanned aircraft.
He also claimed that despite the interception of most incoming missiles, one Iranian projectile evaded Jordan's air defence systems on Friday.
The remarks mark a shift in tone from a U.S. official who had previously sought to play down Iran's military capabilities. The U.S. Central Command had earlier acknowledged that two American soldiers were killed and one was reported missing following Iranian strikes on the Muwaffaq Salti airbase in Jordan.
MNA