Updated 8.50pm

European countries moved to isolate Belarus on Monday by cutting air ties after it provoked an international outcry by forcing a commercial airliner to land so it could arrest an opposition activist.

EU leaders meeting in Brussels eyed proposals to stop Belarus' state airline flying to the bloc and prevent European carriers from using the country's airspace, after several nations started closing air routes.  

The Ryanair flight from Athens to Vilnius carrying dissident journalist Roman Protasevich was diverted while in Belarusian airspace on Sunday over a supposed bomb threat.

Accompanied by a Belarusian fighter jet - on the orders of strongman leader Alexander Lukashenko - the plane landed in the capital Minsk. There, 26-year-old Protasevich, who had been living between Lithuania and Poland, was arrested along with his Russian girlfriend Sofia Sapega.

Western leaders accused Belarusian authorities of essentially hijacking a European plane, while Minsk claimed it had reacted to secure the flight after receiving a threat from Palestinian Islamist group Hamas to blow up the aircraft.

"There will be a very strong answer because it is outrageous behaviour and Lukashenko and his regime have to understand that this will have severe consequences," EU chief Ursula von der Leyen said as leaders from the bloc gathered. 

Proposed summit conclusions seen by AFP envision banning state carrier Belavia from EU airspace and airports, and calling on EU-based airlines to "avoid overflight of Belarus". 

The bloc is also looking to speed up fresh sanctions already in the pipeline over Lukashenko's crackdown on protests in Belarus and expand them to hit key state-run companies. 

The EU's push to punish Minsk came after Britain and Lithuania said they had issued instructions for their countries' aircraft to avoid Belarusian airspace, with London going further by banning Belarus's flagship carrier.

Ukraine said it would halt direct flights between the two countries and over Belarus, while Scandinavian airline SAS, Germany's Lufthansa and Latvia-based regional airline Air Baltic said they would be avoiding Belarusian airspace.

'North Korea in Europe'

Berlin, London and Brussels summoned the Belarusian ambassadors, as exiled opposition leader Svetlana Tikhanovskaya called for an independent probe, new sanctions and for Minsk to be excluded from international aviation bodies.

"An act of state terrorism was carried out and now any passengers flying over Belarus in a civilian aircraft will be in danger," Tikhanovskaya told reporters in Vilnius.

"The regime has turned our country into North Korea in the middle of Europe," she said.

The EU and other Western countries have already imposed a wide range of sanctions on Lukashenko's government over a brutal crackdown on opposition demonstrations that followed his disputed re-election to a sixth term last August.

Together with co-founder Stepan Putilo, Protasevich until recently ran the Nexta telegram channel that helped organise protests that were the biggest challenge to Lukashenko's rule since he took power in the ex-Soviet country in 1994.

Belarus insisted it had acted legally over the grounding of the Ryanair jet, accusing the West of making "unfounded accusations" for political reasons.

Its air force chief said the plane's captain had decided to land in Belarus "without outside interference" and that the pilot could have chosen to go to Ukraine or Poland.

A senior Belarusian transport official said the authorities received a letter claiming to be from Hamas threatening to blow up the plane over Vilnius unless the EU renounced support for Israel.

German Chancellor Angela Merkel dismissed Minsk's explanations as "completely implausible" as the EU pushed for a probe by the International Civil Aviation Organization. The ICAO, a UN agency, is to meet on Thursday.

United Nations Secretary General Antonio Guterres backed calls for a "full, transparent and independent investigation in this disturbing incident". 

'Shocking act'

The diversion of the plane was roundly condemned by other Western allies.

NATO demanded a probe into the "serious and dangerous incident" and alliance envoys were to discuss it on Tuesday.

US Secretary of State Antony Blinken called it "a shocking act" that "endangered the lives of more than 120 passengers, including US citizens".

Belarus's main ally Russia showed little concern, however.

Foreign Minister Sergei Lavrov said Minsk was taking an "absolutely reasonable approach" while ministry spokeswoman Maria Zakharova mocked the Western indignation.

"We are shocked that the West calls the incident in Belarusian air space 'shocking,'" Zakharova said on Facebook, accusing Western nations of "kidnappings, forced landings and illegal arrests".

Britain's Foreign Secretary Dominic Raab raised the possibility of Russian backing for the diversion.

The spiralling tensions around Belarus were in evidence as Minsk expelled the entire staff of Latvia's embassy, including the ambassador, after accusing Latvian authorities of having used an opposition flag at an ice hockey championship.

With close to two million subscribers on Telegram, Nexta Live and its sister channel Nexta are prominent opposition channels and helped mobilise protesters in Belarus.

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

The two were accused of causing mass unrest, an offence punishable by up to 15 years in jail.

UN chief backs 'independent investigation'

Meanwhile, UN Secretary General Antonio Guterres backed calls for an independent investigation, declaring himself "deeply concerned" by the incident.

"The secretary general supports calls for a full, transparent and independent investigation into this disturbing incident and urges all relevant actors to cooperate with such an inquiry," said his spokesman Stephane Dujarric in a statement.

The UN civil aviation agency also announced an "urgent" meeting for Thursday after the international outcry over the landing.

The International Civil Aviation Organization Council's "president has called an urgent meeting of the 36 diplomatic representatives to the ICAO Council" on the flight, the body said on Monday.

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