UK Foreign Secretary Dominic Raab condemned Alexander Lukashenko for his “outlandish actions” and said the UK was working with its allies on a “coordinated” response.
Aircraft have been instructed to avoid Belarusian airspace and Mr Raab said further sanctions are being considered against the Lukashenko administration - including the suspension of energy pipelines in Belarus.
Transport Secretary Grant Shapps said he has instructed the Civil Aviation Authority to request airlines avoid Belarusian airspace "in order to keep passengers safe".
He also suspended the operating permit for Belavia, the country's state-owned airline, effectively banning it from the UK.
It comes after Belarus flagged what turned out to be a false bomb alert to land the plane flying 171 passengers from Greece to Lithuania on Sunday.
They forced the plane to land in their capital city of Minsk before arresting 26-year-old Belarusian journalist and activist Roman Protasevich, pictured below.
Mr Protasevich could face the death sentence after being accused of organising protests against President Lukashenko.
In a strongly worded statement on Monday morning, Mr Raab called for the activists’ release and said: “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. 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 coordinated response, including further sanctions.
“The UK also calls for the ICAO Council to meet urgently to consider the regime’s flouting of the international rules safeguarding civil aviation.”
Mr Raab told MPs on Monday afternoon there were more than 100 passengers on the flight.
"We are urgently seeking full details of precisely what took place in relation to Flight FR4978 but the scenario as reported is a shocking assault on civil aviation and an assault on international law," he said.
"It represents a danger to civilian flights everywhere and it is an egregious and extraordinary departure from the international law and the international practice that guides international civil aviation under the Chicago Convention."
Tom Tugendhat, chairman of the UK Foreign Affairs Select Committee, described the act as “air piracy” and a “hijacking”.
He told BBC Radio 4’s Today programme: “This was a flight between two Nato members and between two EU members – between Greece and Lithuania. And if it’s not an act of war, it’s certainly a war-like act.”
Franak ViaÄorka, a journalist and friend of Mr Protasevich, was in touch with him just before he departed.
Mr ViaÄorka said: “He shared some concerns when he was in the airport in Athens. He saw that someone was following him, so he already felt something bad.
“I’m not sure if it’s related, but he mentioned that there was a guy who was trying to take pictures of his documents and perhaps this also part of a provocation against him.”
Witnesses said the activist was trembling and “super-scared”, telling fellow passengers he would face the death penalty.
Mr ViaÄorka added: “I can’t imagine what’s happening to him right now.”
Lukashenko, who is one of President Putin’s closest allies, “personally ordered” the operation so a dissident on board could be arrested, according to state media.
He has ruled the country since 1994 and cracks down on opposition figures.
The plan to seize Mr Protasevich also appears to have also involved suspected Belarussian KGB agents.
Ryanair’s chief executive Michael O’Leary also said the forced landing was a “state-sponsored hijacking” and added: “It was clear it appears that the intent of the Russian authorities was to remove a journalist and his traveling companion. We believe there was also some KGB agents offloaded from the aircraft as well.”
Western leaders have widely condemned the act. EU leaders are due to discuss their response to what the union’s executive called a “hijacking”.
Ursula von der Leyen, head of the European Commission, warned “the outrageous and illegal behaviour... will have consequences”.
US Secretary of State Antony Blinken condemned the “shocking act” and said President Joe Biden’s administration was “co-ordinating with our partners on next steps”.
Mr Protasevich is a former editor of Nexta an influential opposition channel on messaging app Telegram.
Nexta helped organise protests that erupted in Belarus last August after Mr Lukashenko claimed victory at elections that were widely regarded as rigged.
Mr Protasevich, who left Belarus in 2019 to live in exile in Lithuania, was designated a “terrorist” by Belarus in November over his role in co-ordinating demonstrations.