Belarus forced a Ryanair flight carrying a wanted opposition activist to Vilnius to divert and land in Minsk, provoking a furious outcry from European leaders.

Belarusian state television reported that Roman Protasevich, a 26-year-old opposition blogger exiled in Poland, had been detained in the capital after flight FR4978 was diverted - ostensibly over a security scare.

Poland's Prime Minister Mateusz Morawiecki denounced yesterday's major diplomatic incident as "an act of state terrorism", while French Foreign Minister Jean-Yves Le Drian called for a "strong and united response" from the European Union.

The EU is set to discuss toughening its existing sanctions against Belarus - imposed over the crackdown by the regime of President Alexander Lukashenko on opposition protesters - at a pre-planned summit tomorrow.

After hours grounded in Belarus the flight was able to continue on its journey, landing in Vilnius at 6.25pm GMT, the airport's online arrivals board said.

Officials had yet to confirm whether Mr Protasevich was onboard or had remained in detention in Belarus.

Minsk's airport had released a statement earlier saying the aircraft had to make an emergency landing there at 12.15pm GMT following a bomb scare.

"The plane was checked, no bomb was found and all passengers were sent for another security search," said Nexta, a Belarus opposition channel on the Telegram messaging app, which Mr Protasevich previously edited.

Lukashenko's press service said on its own Telegram channel that the president had given the order to divert the flight and had ordered a Mig-29 fighter jet to accompany the plane.

The incident comes as Belarus authorities intensify their crackdown on the opposition following historic protests that gripped the ex-Soviet country after last year's disputed presidential election.

EU Commission President Ursula von der Leyen said the action would have consequences.

Taoiseach Micheál Martin said on Twitter: "The forced landing of a passenger plane in Belarus today to detain a journalist is absolutely unacceptable.

"These unprecedented actions have caused widespread concern across the EU – and they must be addressed at tomorrow's #EUCO (EU Council)."

Minister for Foreign Affairs Simon Coveney tweeted: "Extremely worrying reports of a Ryanair plane forced to land in Belarus to detain an opposition blogger. We are in contact with the Airline and EU colleagues."

A Government spokesperson said: "We are very concerned by reports from Belarus about a Ryanair flight being diverted to Minsk airport by Belarus authorities.

"Officials from the Department of Foreign Affairs and Department of Transport are in contact with the airline and following events closely. We are also in contact with EU partners. The flight and all passengers should be allowed to resume their journey forthwith."

The diversion of a flight between two EU countries - Greece and Lithuania - and the arrest of an opposition activist who had been onboard, prompted a torrent of outrage from European leaders.

European Council president Charles Michel said he condemned it "in the strongest possible terms" and demanded Protasevich's release.

In Athens, where the flight began, Prime Minister Kyriakos Mitsotakis tweeted: "The forced landing of a commercial plane to detain a journalist is an unprecedented, shocking act.

"We demand all passengers' immediate release," he added, calling for EU action to "step up pressure on Belarus. Enough is enough".

Lithuanian President Gitanas Nauseda described Belarus's actions as "abhorrent", while the French government summoned the Belarusian ambassador to Paris, Igor Fissenko.

NATO called it "dangerous" and demanded an international investigation.

Since last August's disputed election, Belarusians have taken to the streets demanding the resignation of Lukashenko, who has ruled for over two decades.

Protasevich and Nexta founder Stepan Putilo, 22, were added to Belarus's list of "individuals involved in terrorist activity" last year.

The two bloggers - both now based in Poland - were added to the list over charges of causing mass unrest, an offence punishable by up to 15 years in jail.

Belarus had also labelled the Nexta Telegram channels and its logo "extremist" and ordered them blocked.

Nexta Live and sister channel Nexta - with close to two million subscribers on Telegram - are prominent voices of the Belarus opposition and helped mobilise protesters.

"It is absolutely obvious that this is an operation of secret services to capture the plane in order to detain activist and blogger Roman Protasevich," exiled opposition leader Svetlana Tikhanovskaya said on Telegram.

The opposition says that Tikhanovskaya, who fled to neighbouring Lithuania after the election, was the true winner of last year's presidential vote.

Roman Protasevich

A member of the Nexta team, Tadeusz Giczan, said on Twitter that representatives of the Belarusian security agency had been on the flight with Mr Protasevich.

"Then when the plane had entered Belarus airspace, the KGB officers initiated a fight with the Ryanair crew insisting there's an IED onboard," he said.

A spokeswoman for state company Lithuanian Airports, Lina Beisine, told AFP that Minsk airport had said the flight was redirected "due to a conflict between a member of the crew and the passengers".

Ryanair said the flight's crew had been notified by Belarus air traffic control of "a potential security threat on board" and were instructed to divert to Minsk, the "nearest" airport.

Lithuanian Foreign Minister Gabrielius Landsbergis said there were 171 passengers aboard the flight, most of them Lithuanian nationals.

The EU and the United States have sanctioned Lukashenko and dozens of officials and businessmen tied to his regime with asset freezes and visa bans.

The opposition protests in Belarus, which left at least four people dead, have now subsided, but journalists and activists continue to receive prison sentences in the aftermath.