Taoiseach Micheál Martin and other European leaders reacted with outrage after Belarus intercepted a Ryanair flight bound for Lithuania and arrested a top opposition activist on board.
The forced landing of Ryanair flight FR4978 in Belarus to detain a prominent critic of President Alexander Lukashenko will be raised by European leaders at a summit on Monday.
The Taoiseach described the incident as “absolutely unacceptable”.
"These unprecedented actions have caused widespread concern across the EU," Mr Martin said, insisting they be addressed at the European Council meeting.
Mr Lukashenko ordered a MiG-29 military jet to intercept the plane and escort it to Minsk before it left Belarus's air space en route from Greece to Lithuania.
The Ryanair Boeing 737-800 aircraft, carrying 170 passengers, landed after being notified of a possible bomb threat on board. No bomb was found at Minsk.
Lukashenko opponent
During security checks on passengers, police arrested one of the passengers, activist and blogger Roman Protasevich (26), an opponent of Mr Lukashenko whose administration placed him on a terrorist watchlist after he exposed police brutality during anti-government protests last year.
Ryanair said the plane’s crew on the Vilnius-bound flight from Athens were notified by Belarus air traffic control of a “potential security threat on board” and told to fly to the nearest airport.
“Nothing untoward was found,” said Ryanair of the subsequent search and the plane was cleared to leave after about five hours in Minsk. It made no comment about Mr Protasevich, who had been living in exile in Lithuania.
Messages sent by Mr Protasevich, published on the Telegram social media channel he edits, said he had noticed a man following and photographing him at Athens airport.
‘Dangerous incident’
Belarus opposition leader Svetlana Tikhanovskaya, who lost out to Mr Lukashenko in a presidential election last year widely dismissed as rigged, called for the release of Mr Protasevich.
EU Commission president Ursula von der Leyen said the forced landing was “utterly unacceptable”, warning: “Any violation of international air transport rules must bear consequences.”
Nato chief Jens Stoltenberg called it "a serious and dangerous incident".
The International Civil Aviation Organisation, the UN agency, said it was "strongly concerned" the incident could be in breach of international rules on airspace and air safety.
Belarus’s actions were condemned by the UK, French and German foreign ministers.
Poland's prime minister, Mateusz Morawiecki, called for EU leaders to discuss "immediate sanctions" against Mr Lukashenko's regime at Monday's EU summit.
“Hijacking a civilian plane is an unprecedented act of state terrorism – it cannot go unpunished,” he said.