The Defence Force says a weapon went missing in Afghanistan sometime in the last five years when an officer was on a routine patrol, but it says it is highly unlikely insurgents would have been able to use it.
According to the Sunday Star Times the weapon was lost by an officer last year in Bamiyan Province.
The Defence Force says the officer, who was employed in an administrative role, also had the necessary training as an Infantry Platoon Commander to participate in patrols.
It says the man took part in several patrols, including commanding one escort in what the Defence Force says was a "low threat" area.
It says during one of those patrols, a standard semi-automatic rifle was lost, and despite intensive searches, was never recovered.
The Defence Force says the incident happened some stage in the last five years but did not offer a more detailed timeline.
It says the ammunition required for the lost item is hard to come by in Afghanistan, and there is no evidence it got into the hands of rebel fighters.
It says a Court of Inquiry was conducted after the weapon was lost and disciplinary action was taken.