Belarusian opposition leader Pavel Latushka claims his shadow government group, National Anti-Crisis Management, has information showing that two Belarusians and four Russian nationals did not resume the flight to Vilnius.

While detained journalist Roman Protasevich is a Belarus citizen, and his travelling companion Sofia Sapega – who is also detained – is Russian (according to a statement from her university in Vilnius), as our Moscow correspondent Oliver Carroll notes, the identity of the remaining individuals is far from clear-cut.

The Belarusian state aviation agency has said that its air traffic controllers had issued “recommendations” to the crew of the Ryanair plane, but had not forced it to land using threats, according to Russia’s official RIA news agency.

Ryanair’s chief executive Michael O’Leary has accused Belarus of engaging in “state-sponsored piracy”

“This was a case of state-sponsored hijacking … state-sponsored piracy,” Mr O’Leary told Irish Newstalk 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,” he said.

The Belarusian transport ministry has set up a commission to investigate the diversion and landing of a Ryanair plane in the capital Minsk and will publish the results of its investigation soon, according to Russia’s official RIA news agency.

Fury over the events in Belarus has upended the agenda of an EU summit dinner later today, where leaders were due to discuss relations with Russia and the UK but will now also consider punitive steps against Minsk.

The EU’s foreign policy chief Joseph Borrell described the diversion of a plane between two EU states as “an inadmissible step”, saying in a statement: “The EU will consider the consequences of this action, including taking measures against those responsible”

EU Commission president Ursula von der Leyen also tweeted on Sunday that “the outrageous and illegal behaviour of the regime in Belarus will have consequences”.

The EU has already imposed three rounds of sanctions on Belarus in response to last year’s contested presidential election there, and even before the Ryanair incident had been working on a fourth round targeting senior officials, Reuters reports.

According to an EU official, additional sanctions could now include suspending overflights of all EU airlines over Belarus, banning Belarusian airline Belavia from landing at EU airports or suspending all transit, including ground transit, from Belarus to the EU.

In a joint statement yesterday, the chairs of parliamentary foreign affairs committees in the UK, US, Lithuania, Germany, Ireland, Czech Republic, Poland, Estonia and Latvia condemned what they called an “act of state terror”.

Calling for an immediate inquiry by the International Civil Aviation Organisation, they said: “Until ICAO has reported, we call for Belarus to be suspended from the organisation and a ban on all overflight of Belarus including flights to and from the country.

“It is clear that the current administration in Minsk has no respect for the safety of our citizens and cannot be trusted to defend their rights. This act of state terror and kidnapping is a threat to all those who travel in Europe and beyond. It cannot be allowed to stand.”

They called for sanctions to be placed on Belarus and for the immediate release of the detained journalist Roman Protasevich.

A Belarusian university in Vilnius said its student Sofia Sapega, 23, has also been detained in Minsk and is demanding her release.

The detention of Ms Sapega – a Master’s student who the university said had been on holiday in Greece with journalist Roman Protasevich – was confirmed by her family, the European Humanities University (EHU) told Reuters.

A Lithuanian passenger, who gave his name only as Mantas, said that upon on hearing the news the plane was being diverted, Mr Protasevich pulled a laptop and a phone from the overhead locker and gave them to a female companion. On landing, Mr Protasevich was immediately separated, Mantas said.

Ms Sapega, who is a Russian citizen, was flying to Vilnius to defend her Master’s thesis at the university to graduate from her five-year course, the university said in a statement.

“As a result of a cover operation by the Belarusian authorities, the student was detained by the Administration of the Investigative Committee for the city of Minsk on groundless and made-up conditions,” the statement said.

“We protest against the unjustified detention of the member of EHU community,” it added.

With international outcry growing this morning, our veteran travel correspondent Simon Calder believes there could be serious implications for Belarus:

For those of you just catching up on this story now, here’s our report from Sunday evening:

Good morning, we’ll be using this liveblog to follow the latest developments after a Ryanair passenger jet carrying a dissident journalist was dramatically grounded in Minsk.