The Army on Wednesday evening identified the fifth American service member who was killed in the Iran conflict this week as Major Jeffrey O’Brien from Waukee, Iowa.

The sixth and final person's identity has not been confirmed, but the War Department said in a separate release that it believes the sixth casualty is 54-year-old Chief Warrant Officer 3 Robert Marzan of Sacramento, California.

The identities come the day after the Pentagon identified the other four American service members who were killed in Kuwait on Sunday. The six service members are considered the first U.S. casualties in the conflict in the Middle East. 

The Army said all six soldiers were assigned to the 103rd Sustainment Command from Des Moines, Iowa, and were killed at the Port of Shuaiba, during an unmanned aircraft system attack.

The service said O'Brien, who was 45-years-old, was commissioned in the Army Reserve as a Signal Corps Officer in 2012 and was stationed in Kuwait in 2019. 

He has been decorated with the Army Achievement Medal, Meritorious Unit Commendation, Army Superior Unit Award, Army Reserve Component Achievement Medal, National Defense Service Medal, Global War on Terrorism Expeditionary Medal, Army Service Ribbon, and the Armed Forces Reserve Medal with “M” Device.

Details on Marzan were not immediately clear, but the Pentagon said his identity will need to be confirmed by the Army's medical examiner. Marzan is believed to have been on the scene at the time of the March 1 attack.

"If you kill Americans — we will hunt you down, and we will kill you," Pentagon spokesperson Sean Parnell said on X on Tuesday. "Iran is learning the hard way that President Trump means what he says."