Two more US naval aircraft flew over Irish sovereign airspace on Tuesday while tracking a ship in the North Atlantic, which attempted to collect oil from Venezuela last month.
The first Poseidon anti-submarine aircraft flew over a patch of sea just off the northern tip of Co Donegal at about 5.30pm, travelling between the mainland and the island of Inishtrahull.
A second aircraft entered Irish airspace after 8pm, around Wexford, en route to the Atlantic.
It is not clear if official permission was sought from the Irish Government for either flight.
A similar aircraft flew over the middle of Ireland on Monday before returning to its UK base via the same route.
Under long-standing Irish policy, foreign military aircraft are not permitted to use Irish airspace while on active military operations.
Irish and US sources said permission had been sought for Monday’s flight at Government level and it also received clearance from Irish air traffic control.
The Department of Foreign Affairs did not immediately respond to a query on whether the aircraft from the flights on Monday and Tuesday had been granted permission to fly through Irish airspace.
The aircraft were headed for a location in the North Atlantic containing the Marinera, a sanctioned oil tanker which US forces have pursued for almost three weeks.
The tanker had initially been on course to skirt the edge of Irish economic waters on its journey north. However, it has since moved further out into the Atlantic and is now in a position roughly halfway between Ireland and Iceland.
[ US military monitors oil tanker off Irish coast as it sails towards RussiaOpens in new window ]
The ship made the manoeuvre before CNN and CBS, citing unnamed sources, reported on Monday night that US forces still intend to seize the ship by force.
The situation is further complicated by the fact that the Marinera has claimed the protection of Russia since changing its registration to that country last month, while US forces were pursuing it.
Moscow has responded by asking the US to call off its pursuit. On Tuesday, the Russian foreign ministry said the ship is sailing under the Russian flag and is in compliance with international law.
The RAF also launched maritime surveillance aircraft in the area containing the Marinera on Tuesday. These remained outside Irish airspace at all times.
On Tuesday, Tánaiste Simon Harris said he was not aware whether permission had been sought for the flight over Ireland by the US military aircraft on Monday.
He told reporters there were “very clear rules in relation to planes from other jurisdictions accessing Irish airspace … I would imagine that those rules would certainly have been followed.”
[ Irish military aircraft sent to monitor fleeing oil tankerOpens in new window ]
Asked about the implications of such flights for Ireland’s neutrality, Mr Harris said the Republic is neutral and not militarily aligned.
“That doesn’t mean that we’re in any way immune from or unconcerned about security,” he said. “Nor do we generally comment on those matters, for obvious reasons.”
Elsewhere, Minister for Higher Education James Lawless said he would have no particular concern about the State allowing a US plane to overfly it as part of a military operation. He said he did not know enough about the flight on Monday to comment on it in any detail.
“I think that there is inevitably going to be a degree of co-operation with partners, whether that’s Europe, whether that’s [the] United States, whether it’s the UK, it could be Japan tomorrow, the countries that are still in our orbit. I don’t have any particular concern about that at all,” said Mr Lawless.
He said he was more concerned about the fact that a “Russian shadow tanker” could get so close to Ireland, citing both environmental and security concerns.