A US military plane spent a number of hours circling in Irish airspace on Tuesday afternoon.
It was picked up by an app designed to identify commercial aircraft, as it conducted a number of circuits over the island at a height of about 28,000 feet.
The Irish Aviation Authority said in a statement that a military aircraft with a pre-filed flight plan operated in Irish airspace, and that it had pre-approval from the Department of Foreign Affairs.
The nature of the flight is unclear.
The Department of Foreign Affairs said that there were 13 overflights by unarmed US military aircraft without prior permission in August.
The Department said: "Under long-standing arrangements we permit US military aircraft to overfly Ireland without seeking prior permission provided they are unarmed, carry only cargo and comply with navigational requirements."
The US embassy in Dublin said: "The US government is appreciative of the Irish Government's policy of granting permission on a case by case basis for the transit of US service members and aircraft through Ireland.
"The US government appreciates and respects the conditions under which planes can utilize Irish airspace in accordance with Irish law."
The Irish Aviation Authority (IAA) have confirmed: "A US military aircraft with a pre-filed flightplan operated in Irish airspace on Tuesday and was pre-approved by the Department of Foreign Affairs in the normal manner".
Security Analyst, Dr Tom Clonan, said that there could be several reasons for this.
He said: "It could have been a training flight...it could have been because maybe US VIP flights passing through our controlled airspace or - and I think this is probably the most likely explanation - we have had other visitors to our airspace in recent times.
"We had Russian aircraft bombers enter our controlled airspace recently down the west coast.
"In the last number of years, with the Ukraine and rising tensions in the Balkans, some of the old Cold War rhetoric has found its way back into the international foreign relations narrative."