The Pentagon had earlier announced a US troop died during an IS attack on a Peshmerga position north of Mosul.
“It was an orchestrated attack with shots and multiple IEDs (bombs) going off,” the official told AFP, speaking on condition of anonymity.
Another defense official had earlier said the serviceman was killed by “direct fire.”
Arizona Governor Doug Ducey identified the fallen SEAL as Charlie Keating IV of Phoenix.
Pentagon press secretary Peter Cook said the attack took place about three to five kilometers (two to three miles) behind the forward line of troops, adding that the troop was advising and assisting Peshmerga forces.
“This sad news is a reminder of the dangers our men and women in uniform face every day in the ongoing fight to destroy ISIL and end the threat the group poses to the United States and the rest of the world,” Cook said, using an acronym for the IS group.
“Our coalition will honor this sacrifice by dealing ISIL a lasting defeat.”
Special operations forces are playing a key role in America’s campaign against the IS group in Iraq and Syria.