Michael O'Leary says the forced diversion of a Ryanair flight to Belarus was a "state-sponsored hijacking".
The airline's CEO says it appears authorities removed a journalist and his travelling companion from the plane, while they also believe there were some KGB agents on board the flight.
The plane - which was flying from Greece to Lithuania - was escorted by a Belarusian fighter jet after reports it had explosives on board, but none were found.
It was forced to divert from Minsk, where an opposition blogger - Roman Protasevich - was arrested.
European leaders will discuss a response to the incident today, after several officials described it as "utterly unacceptable".
Foreign Affairs Minister Simon Coveney has described it as "aviation piracy that's state-sponsored".
On Newstalk Breakfast, Mr O'Leary said he thinks it's the first time such an incident has happened to a European airline.
He said: "This was a case of state-sponsored hijacking… state-sponsored piracy.
“We’re debriefing our crew, who did a phenomenal job to get that aircraft and almost all the passengers out of Minsk after six hours."
Mr O'Leary said the incident was "very frightening" for passengers and crews, as they were held under armed guard and had their bags searched.
He said: "It appears the intent of the authorities was to remove a journalist and his travelling companion… we believe there were some KGB agents offloaded at the airport as well."
There are growing calls from European politicians - including in Ireland - for flights to be banned from flying over Belarus.
Mr O'Leary said his airline will take guidance from European authorities about whether that should happen.
However, he said they don't fly over Belarus much - and it would be a "very minor adjustment" to fly over Poland instead.
"Aviation piracy"
Minister Coveney, meanwhile, says the plane was "effectively ordered" to land in Minsk.
He said: "Five or six people left the plane, but only one of them was arrested - which would suggest the others were secret service people.
He said there are lots of people who are opponents of Belarusian President Alexander Lukashenko - a leader who Minister Coveney said has "no democratic legitimacy".
He said: "There's a European Council meeting starting this evening... I think you will see decisions taken by the EU to increase the level of sanctions against Belarus, and perhaps to link that to aviation.
"I think if the EU doesn't respond firmly and directly, then I think that will be seen by Belarus as weakness on behalf of the EU."
