A Defence Forces spokesman has confirmed that the video of two Irish soldiers 'mock' aiming their machine guns at local people in Liberia was posted by a soldier.
He is being interviewed by military police as part of the Defence Forces investigation into the video.
Army spokesman Commandant Gavin Young said the incident was 'totally unacceptable,' and added that those involved could face serious disciplinary action.
Officers believe the footage was taken in the last 18 months in Liberia in West Africa.
It is thought that all of those involved in the incident were aware it was a prank.
However, the Defence Forces say they are taking a dim view of the incident because any misuse of weapons is taken seriously.
The footage was posted on YouTube in the past few days but the army has since had it removed.
The last unit of Irish troops serving in Liberia as part of a United Nations peacekeeping mission arrived home last night.
The remaining 83 soldiers from the 96th Infantry Battalion were met by their families and friends.
The Irish had been serving in the west African country for the past three and a half years.
Seven battalions of Irish peacekeepers had served there on six-month tours of duty, with each group consisting of 400 soldiers.
As these soldiers were welcomed home, 200 Irish peacekeepers continue to serve in Kosovo and 150 in Lebanon.
The Irish contingent formally handed over its role to Pakistani troops earlier this month.