Ryanair has accused Belarus of having spies on board a passenger flight that was forced to land in the country's capital as part of a claimed plot to detain an opposition activist.
The plane, carrying 171 passengers from Greece to Lithuania, was nearing the end of its journey when Belarus air traffic control warned the crew there may be a bomb on board.
A fighter jet was sent to divert the plane to the Belarusian capital of Minsk, even though it was not the closest airport.
When it landed, opposition journalist Roman Protasevich, 26, was arrested by state security service officers.
Protasevich is wanted in Belarus on extremism charges and allegations of inciting riots, which he denies.
He spoke on a video posted later on Monday to several channels on the Telegram messaging app, which is popular in the country.
It included Protasevich admitting to organising large protests in Minsk last year.
His father, Dzmitry Protasevich, told Reuters that he believed it was a forced statement.
"It's not his words, it's not his intonation of speech," Mr Protasevich said. "He is acting very reserved and you can see he is nervous.
"And it's not his pack of cigarettes on the table. He doesn't smoke these. So I think he was forced."
He also believed his son was beaten in custody.
"My son cannot admit to creating the mass disorders because he just didn't do any such thing," he said.
US President Joe Biden said late on Monday night, after the video was released: "This outrageous incident and the video Mr Protasevich appears to have made under duress are shameful assaults on both political dissent and the freedom to the press.
"The United States joins countries around the world in calling for his release."
Ryanair chief executive Michael O’Leary said he believed that Belarusian KGB agents were on board the flight.
“It is a case of state-sponsored hijacking,” Mr O'Leary told Irish radio.
"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."
Meanwhile, Lithuania said five passengers on board the flight did not reach their final destination, further raising suspicions that security service personnel were on board.
UK Foreign Secretary Dominic Raab on Monday said Russian involvement was a distinct possibility.
"I'll be careful what I say at this point, because … it's very difficult to believe that this kind of action could be taken without at least the acquiescence of the authorities in Moscow," Mr Raab said.
"But as I say, it is unclear as yet."
The EU reacted with anger and called for an international investigation into what it said was a hijacking.
Britain said Belarusian President Alexander Lukashenko should be held to account for his "outlandish actions".
UN Secretary General Antonio Guterres called for a “full, transparent and independent investigation into this disturbing incident and urges all relevant actors to co-operate with such an inquiry", said his spokesman, Stephane Dujarric.
Meanwhile, Britain's Transport Secretary Grant Shapps instructed the Civil Aviation Authority to request that airlines avoid Belarusian airspace for passenger safety, and he suspended the operating permit of the Belarus national carrier Belavia.
The European Council of 27 nations were due to meet later on Monday to discuss the issue.
State media reported that Mr Lukashenko gave the order to send in the warplane.
The incident drew condemnation from around the world, with countries and the UN demanding the immediate release of Protasevich.
EU Commission President Ursula von der Leyen said the “outrageous and illegal behaviour” would have consequences.
“Those responsible for the Ryanair hijacking must be sanctioned,” Ms von der Leyen said.
Mr Raab said Sunday's action would have “serious implications”.
“The UK condemns yesterday’s actions by the Belarusian authorities, who arrested journalist Roman Protasevich on the basis of a ruse, having forced his flight to land in Minsk," he said.
"Mr Lukashenko must be held to account for his outlandish actions.
“The UK calls for the immediate release of Mr Protasevich and other political prisoners held in Belarus.
"The UK is working with our allies on a co-ordinated response, including further sanctions."
Mr Biden condemned "the diversion of the plane and the subsequent removal and arrest of Mr Pratesevich".
"I join the many calls for an international investigation to ascertain the complete facts of the case," he said.
Earlier, US Secretary of State Antony Blinken condemned the "shocking act" and said the Biden administration was "co-ordinating with our partners on next steps".
“Initial reports suggesting the involvement of the Belarusian security services and the use of Belarusian military aircraft to escort the plane are deeply concerning and require full investigation," Mr Blinken said.
Belarus opposition leader Sviatlana Tsikhanouskaya said the whereabouts of Protasevich were unknown.
"We still don't know where he is and in what state," Ms Tsikhanouskaya said.
"There is a high probability that he is undergoing torture by the special services at this very minute."
Tom Tugendhat, chairman of the UK’s foreign affairs committee, called for all civilian airlines to stop flying over Belarus.
"Our own citizens are in very grave danger even if they are not being specifically targeted by the Lukashenko regime," Mr Tugendhat told BBC Radio 4.
"Anybody who is willing to put MiG fighters into the air to force a civilian aircraft to the ground is clearly not averse to using force to bring it down."
He said the Yamal-Europe pipeline, which supplies natural gas to several European nations, should feature in sanctions on the Belarus regime.
"It’s clearly no longer acting simply as a rogue administration that lost an election last year and continued in office, but as a state sponsor of terror and we simply cannot tolerate that," Mr Tugendhat said.
"This is an act of air piracy, combined with hijacking and eventually linked to kidnapping."
Former Polish foreign minister Radek Sikorski said Belarus should answer charges at the International Criminal Court.
Mr Sikorski said western leaders should impose sanctions on Russian President Vladimir Putin, a close ally of Mr Lukashenko.
“The concern should be for the two passengers who were seized in Minsk after this threat to EU citizens,” he said.
“If it’s true that the MiG fighter threatened a civilian aircraft with being shot down in order to seize an EU-protected person, this is completely outrageous and we cannot let it pass.
"Belarus has abused international norms in the area of air travel."
Protasevich worked for online news service Nexta last year when it broadcast mass protests against Mr Lukashenko.
The president, who has ruled the country since 1994, has cracked down on dissenting voices since winning a disputed election last year.
A passenger on board the aircraft said Protasevich had his head in his hands and was shaking when he realised the flight was being diverted to Minsk.
As he was led away, he reportedly said: "I'll get the death penalty here.”
The passenger said: “When it was announced that we're going to land in Minsk, Protasevich stood up to open the luggage door.
"He took his luggage and tried to split up his things, like he gave his computer and iPhone to his girlfriend."
Another passenger on the plane, Edvinas Dimsa, said the journalist was “very much afraid”.
“It looked like if the window had been open, he would have jumped out of it,” Ms Dimsa said.
After seven hours in Minsk, the flight took off again and landed in Vilnius, Lithuania.
Ryanair said shortly after the incident 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".
It said “nothing untoward” was found on the plane and it landed safely in Vilnius. The airline made no mention of Protasevich's arrest.
Irish Foreign Minister Simon Coveney said the “utterly unacceptable” diversion should be met with a strong response.
“This is an Irish airline with EU citizens on board, forced to land in Minsk, while travelling between EU cities,” Mr Coveney said.
“A strong and united response from EU needed. EU inaction or indecision will be taken as weakness by Belarus.”
Lithuanian President Gitanas Nauseda agreed Belarus must face consequences.
"It should be noted that such attacks on the opposition have recently become systematic," Mr Nauseda said.
"I am attending the European Council tomorrow and we will no doubt raise this issue as well. It's time to stop communicating with the regime just by making declarations.
"Concrete measures are needed, capable of changing the behaviour of the Belarusian regime."
Human rights groups say about 35,000 people have been detained in Belarus since August.