A witness told AFP that Protasevich told fellow passengers he would face the death penalty.
"He was not screaming, but it was clear that he was very much afraid", another passenger, Edvinas Dimsa, recalled, according to AFP. "It looked like if the window had been open, he would have jumped out of it".
Lithuanian President Gitanas Nauseda said he would propose banning Belarusian planes from European Union airports and "serious sanctions" against Mr Lukashenko's government for what he described as a "state-sponsored terror act".
ICAO has no regulatory power, but sits at the centre of a system of safety and security standards that are managed through the Montreal agency by its 193 member states, including Belarus.
Lithuanian President Gitanas Nauseda called for an worldwide response.
Exiled opposition leader Sviatlana Tsikhanouskaya called on the International Civil Aviation Organization to begin an investigation.
Minsk's airport had released a statement earlier saying the plane had to make an emergency landing there at 1215 GMT following a bomb scare.
The presidential press service said the bomb threat was received while the plane was over Belarusian territory; officials later said no explosives were found on board.
It 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.
Mr Michel in a separate statement called for Protasevich to be released.
"Belarus must ensure safe return of crew and all passengers", he said.
He added on Twitter, "We demand an global investigation and are coordinating with our partners on next steps".
European leaders reacted with fury. He called it a "brazen and shocking act to divert a commercial flight and arrest a journalist". The Belarusian Interior Ministry said Raman Pratasevich was arrested at the airport.
Antony Blinken, the US secretary of state, sharply criticized the government of Belarus on Twitter on Sunday for its detention of Protasevich.
The widely condemned tactic was the latest attempt by Alexander Lukashenko, the country's authoritarian leader, to suppress the influential voice of Protasevich.
The two - both now based in Poland - were accused of causing mass unrest, an offense punishable by up to 15 years in jail.
The journalist, who now works for a different Telegram channel called Belamova and who describes himself on Twitter ironically as the first "journalist-terrorist" in history, is based in Lithuania.
With close to 2 million subscribers on Telegram, Nexta Live and its sister channel, Nexta, are prominent opposition channels and helped mobilize protesters.
Belarus police detain journalist Raman Pratasevich, center, in Minsk, Belarus.
The opposition says that Tikhanovskaya, who fled to neighboring Lithuania after the election, was the true victor of last year's presidential vote.
Roman Protasevich during a court hearing.
"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.
Roman Protasevich, 26, was arrested after his flight from Athens was diverted from its scheduled destination of Vilnius in Lithuania on Sunday.
Ryanair said its flight that was forced to land and spend a number of hours on the ground in Belarus on Sunday arrived safely in the Lithuanian capital of Vilnius at 1825 GMT.
The US, EU, Britain and Canada have already imposed travel bans and frozen the assets of nearly 90 Belarusian officials, including Mr Lukashenko.