A Ryanair plane from Greece to Lithuania was diverted to Belarus for several hours on Sunday, with activists saying it was done to arrest a dissident journalist on board.
European nations reacted with outrage, accusing Belarus of "state terrorism".
The ex-editor of the Nexta group, Roman Protasevich, was detained before the plane was allowed to resume its flight.
Belarus media said a MiG-29 escorted the jet to Minsk because of a bomb scare but no explosives were found.
The plane finally landed in the Lithuanian capital, Vilnius, its original destination, at 21:25 local time (18:25 GMT), more than seven hours after its scheduled arrival.
Arriving passengers said they had been given no information about the reason for the abrupt diversion to Minsk. One said Mr Protasevich looked "super scared. I looked directly to his eyes and it was very sad".
Another, Monika Simkiene, told AFP news agency: "He just turned to people and said he was facing the death penalty."
There have already been calls for the EU and Nato to intervene.
UK Foreign Secretary Dominic Raab warned the "outlandish action" would have "serious implications".
Belarus opposition leader Svetlana Tikhanovskaya, who was beaten by Alexander Lukashenko in presidential polls last year widely denounced as rigged, was among those demanding Mr Protasevich's release.
Since August's election, 66-year-old Mr Lukashenko, who has ruled the country since 1994, has cracked down on dissenting voices. Many opposition figures have been arrested or, like Ms Tikhanovskaya, fled into exile.
How was the flight diverted?
Flight FR4978 was en route from Athens to Vilnius when it turned east to Minsk shortly before it reached the Lithuanian border. Greece and Lithuania put the number of passengers on board at 171.
In a statement, Ryanair said that the crew had been "notified by Belarus (Air Traffic Control) of a potential security threat on board and were instructed to divert to the nearest airport, Minsk".
The flight path, visible on the Flightradar24 website, suggests the plane was actually nearer to Vilnius than Minsk when it turned.
Ryanair said checks in Minsk found "nothing untoward" and the aircraft left Minsk at 20:50 local time.
"We apologise sincerely to all affected passengers for this regrettable delay which was outside Ryanair's control," it added.
The Ryanair statement made no mention of Mr Protasevich.
Nexta was the first to break the news of his arrest. It said the plane and its passengers was searched, then Mr Protasevich was taken away.
Belta, the state-owned news agency in Belarus, said Mr Lukashenko had personally given the order for the plane to land in Minsk following the bomb alert, and approved despatching the MiG-29 fighter jet.
What has the reaction been?
It has been angry and it is growing.
The US ambassador to Belarus, Julie Fisher, tweeted that it was "abhorrent" Mr Lukashenko had faked a bomb threat and sent fighter jets to arrest a journalist.
Lukashenka and his regime today showed again its contempt for international community and its citizens. Faking a bomb threat and sending MiG-29s to force @RyanAir to Minsk in order to arrest a @Nexta journalist on politically motivated charges is dangerous and abhorrent.— Julie Fisher (@USAmbBelarus) May 23, 2021
European Council chairman Charles Michel said EU leaders would discuss "this unprecedented incident" on Monday at a Council summit and it would not "remain without consequences".
Nato Secretary General Jens Stoltenberg said this was a "serious and dangerous incident".
Both Latvia and Lithuania said the airspace over Belarus should be recognised as unsafe, with Latvia's Foreign Minister Edgars Rinkevics saying it should be closed to all international flights.
Today’s hijacking of #Ryanair flight by Lukashenko regime shows that Belarusian airspace is not safe, people’s lives were put at risk and kidnaping of a political opponent took place. Belarusian airspace must be closed for all international flights.— Edgars Rinkēvičs (@edgarsrinkevics) May 23, 2021
The UN's agency for civil aviation, ICAO, said it was concerned about an "apparent forced landing" which could be "in contravention of the Chicago Convention" which sets out the rules on airspace and aircraft safety.
Poland's Prime Minister Mateusz Morawiecki said: "Hijacking a civilian plane is an unprecedented act of state terrorism that cannot go unpunished."
We do not yet know the full details of this story but its implications could be huge.
There are questions about freedom of the air: how vulnerable may other flights be to this kind of behaviour? Some are already calling it an act of aggression or state terrorism, a form of hijacking. In how much danger were the passengers placed? What precedent may be set? Should flights be diverted away from Belarus airspace?
There are questions for international law: to what extent was this act unlawful, as many presume, and if so, what consequences should there be? There are questions about freedom of speech: will critics of other authoritarian regimes fear this could happen to them?
And there are questions for international diplomacy. Political figures across Europe have already called for the EU and Nato to intervene. There are demands for further sanctions to be imposed on the government of Belarus, whose legitimacy is questioned by many in the West after disputed elections last year. President Lukashenko is often described as Europe's last dictator. Will the word "pirate" now be added to his list of titles?
Who is Protasevich and what is Nexta?
Nexta is a media operation with a Telegram channel, and has visibility on Twitter and YouTube.
It played a key role for the Belarus opposition during the election and has continued to so in its aftermath, particularly with the government imposing news blackouts.
Ms Tikhanovskaya said Mr Protasevich, 26, had left Belarus in 2019 and covered the events of the 2020 presidential election with Nexta, after which criminal charges were filed against him in Belarus.
She said he faced the death penalty in Belarus as he has been categorised as a terrorist.
Western leaders have backed Ms Tikhanovskaya, who claimed victory in the election before she was forced to leave for Lithuania. She had become a candidate after her husband was jailed and barred from running.
Tens of thousands of protesters thronged the capital Minsk for months last year, furious at Mr Lukashenko's declaration of victory. There have been numerous cases of police brutality and some 2,700 prosecutions this year alone.