It has been confirmed that a US spy plane made several round trips over Ireland earlier this week.

The plane flew over Dublin to Shannon to Cork, and then back to Dublin again in a triangular formation for five hours.

It was spotted by a Newstalk listener using the Plane Finder app,

The plane's transponder - which sends certain information to receivers on the ground - showed it to be a Boeing E6 Mercury, belonging to the US Navy.

It is now believed it may have been a Boeing E3 aircraft.

The plane stayed at a constant 28,000 feet throughout its journey over Ireland, and stayed over land for the vast majority of the time.

The Department of Foreign Affairs say: "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".

It says it was notified of 13 such overflights in August.

This image shows the plane (in blue) and its flightplan over Ireland | Image: Plane Finder app

While the US embassy in Dublin say: "The US government is appreciative of the Irish Government's policy of granting permission on a case by case basis for the transit of U.S. 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 says there could be several reasons for this, but that it was an unusual development.

"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", he told Newstalk Lunchtime.

"We had Russian aircraft bombers enter our controlled airspace recently down the west coast...and 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".