A Belarusian journalist arrested after the Ryanair plane he was travelling on was forced to land in Minsk in a "state-sponsored hijacking" has appeared in a new video.
Roman Protasevich has not complained of ill health at a detention centre, authorities in Belarus said.
In a video posted online, Mr Protasevich said he is being treated well and that reports of heart problems are false.
It was not immediately possible to verify whether the words were his own and had not been recorded under duress.
Minsk scrambled a warplane to escort Flight FR4978 on Sunday, flagging a bomb alert that proved false once the plane had made an unscheduled landing where authorities arrested Mr Protasevich, a blogger critical of Belarusian leader Alexander Lukashenko.
Foreign Secretary Dominic Raab said it is “very difficult to believe” the detention of a prominent critic of the Belarus regime could have taken place “without at least the acquiescence of the authorities in Moscow”.
Aircraft have been instructed to avoid Belarusian air space following the incident which has been condemned in the west.
Mr Raab said that although the situation was not yet clear, the relationship between Minsk and Moscow suggested Russian leaders may have been aware of the plans in advance.
Responding to the SNP’s Alyn Smith in the Commons, Mr Raab said: “We don’t have any clear details on that and I’ll be careful on what I say at this point.
“But, as he says, it’s very difficult to believe that this kind of action could have been taken without at least the acquiescence of the authorities in Moscow, but, as I say, it’s unclear as yet.”
Speaking to reporters later he was asked why he believed it could not have taken place without Russia being aware, and Mr Raab replied: “Based on all the circumstances. But we don’t know – it is just the proximity of the relationship between Minsk and Moscow.”
He said further sanctions are being considered against President Alexander Lukashenko’s administration – including the suspension of energy pipelines in Belarus – and the country’s ambassador in London had been summoned for a dressing down.
Transport Secretary Grant Shapps instructed the Civil Aviation Authority to request airlines avoid Belarusian air space “to keep passengers safe”.
He also suspended the operating permit for Belavia, the country’s state-owned airline.
The European Union has joined the UK in new sanctions against Belarus as pressure mounts on Minsk.
A special meeting of the EU Council was held on Monday evening, hours before an already-planned summit, with the 27 members states agreeing to ban Belarusian airlines from EU airspace and airports, and recommending EU airlines do not fly to the country.
Mr Protasevich was on board the flight from Athens to Vilnius when it was forced to change course to head for Minsk after a bomb scare, escorted by a MiG fighter jet.
Ryanair boss Michael O’Leary said it was a “state-sponsored hijacking” and claimed agents from Russia’s KGB were on board the flight.
“I think it’s very frightening for the crew, for the passengers who were held under armed guard, had their bags searched,” he told Newstalk.
“It was clear it appears that the intent of the Russian authorities was to remove a journalist and his travelling companion. We believe there was also some KGB agents offloaded from the aircraft as well.”
Mr Raab told MPs 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.”
A UK Civil Aviation Authority spokesperson said all foreign carrier permits held by Belarusian operators had been suspended until further notice.
They said: “This suspension applies to both scheduled operators, including the Belarusian airline Belavia, as well as chartered air carriers.
“The Civil Aviation Authority has also issued a notice to all UK-registered airlines requesting that they avoid overflight of any territory of the Republic of Belarus.”
Mr Raab called for the release of Mr Protasevich from the “spurious charges” he faces.
“Mr Lukashenko’s regime must be held to account for such reckless and dangerous behaviour,” he added.
He said the UK is working to explore “every potential diplomatic option” and is “actively considering and co-ordinating with our allies on further sanctions on those responsible for this outlandish conduct”.
Tom Tugendhat, chairman of the Foreign Affairs Select Committee, asked the Government to call for the suspension of energy pipelines in Belarus.
He said the Government is “absolutely right” to impose the restrictions on flights and asked: “Will he also go one step further and will he call for a suspension of the Nord Stream 2 pipeline and the Yamal energy pipeline that flows through Belarus, which is where the money comes from that supports this tyrannous regime?”
Mr Raab said on Nord Stream and “other possibilities” that “we will consider and consult with our partners and see what further action they are willing to take as well”.
Shadow foreign secretary Lisa Nandy told the Commons: “For a state to hijack a civilian airliner flying between two Nato allies in order to arrest a journalist is an assault on the freedoms of the air and on freedom of speech.
“Unless the consequences are swift, robust and co-ordinated it will create an extraordinarily dangerous precedent that will put journalists, dissidents and activists from the UK or anywhere else at risk every time they board a plane.”