"This astonishing episode constitutes a new phase in the Belarusian authorities campaign of repression against journalists and civil society in general", Colville said.
European leaders are debating "severe consequences" for Belarusian authorities a day after a Ryanair flight was forced to land in Minsk before opposition journalist Roman Protasevich, who was onboard, was arrested.
Belarus forced a plane carrying an opposition activist to land in its capital, provoking a furious outcry from world leaders who described it as an "act of state terrorism" ahead of an European Union summit expected to toughen sanctions on Minsk. Belarusian state TV posted a video of Protasevich "confessing" to planning riots on Monday.
With dark markings visible on his forehead, he said he was being treated "according to the law".
The comments were immediately dismissed by his allies as having been made under duress.
According to the conclusions of the special European Union summit on Monday, the 27-member bloc strongly "condemned the incident" which "endangered aviation safety" and called on the International Civil Aviation Organization to urgently investigate "this unprecedented and unacceptable incident".
"We will not tolerate that they play Russian roulette with the lives of innocent civilians", he added.
The United States and European countries have called it "air piracy" and "state-sponsored hijacking".
The EU and other Western countries also called for the release of Protasevich, who was detained when the plane landed. From now - no one flying over Belarus - can be secure.
The UN rights office also demanded the immediate release of Protasevich and his girlfriend Sofia Sapega, who was also arrested.
Protasevich, 26, was a co-founder of the Nexta Telegram channel, which helped organise the protests a year ago that were the biggest challenge to Lukashenko's long rule. The channel and another NEXTA Live have over 2 million subscribers and during the protests helped coordinate demonstrations and published videos of them and of police violence that helped catalyze the peaceful uprising against Lukashenko.
Protasevich and Putilo were added to Belarus's list of "individuals involved in terrorist activity" previous year.
In a call with US National Security Advisor Jake Sullivan, Tikhanovskaya asked the United States to "isolate the regime and pressure it through sanctions", she said on Twitter.
Still, the options for Western retaliation appear limited.
A Belarusian MiG-29 fighter jet was scrambled as an escort in a brazen show of force by Mr Lukashenko, who has ruled the country with an iron fist for over a quarter of a century and has close ties to Russian leader Vladimir Putin.
Belarus lies on the flight path of routes within Europe and between Europe and Asia, and skirting Belarus would slow flights down and cost airlines money.
Canada announced sanctions against 55 Belarusian officials previous year after an election that Ottawa said was "marred by widespread irregularities" and a "systemic campaign of repression" and human rights violations under President Alexander Lukashenko.
Lukashenko denies election fraud.
He said: "I think he was forced". "I truly hope that the worldwide community will wake up for him".
They also said the bomb threat supposedly came from the Palestinian terrorist group Hamas in an email addressed to Minsk airport.
Belarus said its ground controllers had given guidance to the flight but had not ordered it to land. In it, she said she had been working as the editor of a Telegram channel that revealed personal data about Belarus' security officers amid the protests.
Ryanair's CEO, Michael O'Leary, on Monday condemned Belarus' actions, telling the Irish radio station NewsTalk "this was a case of state-sponsored hijacking".
It remained unclear why the specific passengers got off at Minsk.
US President Joe Biden slammed the forced diversion of the plane and arrest of Protasevich as "a direct affront to worldwide norms" and said the video appeared to have been made "under duress".
U.S. President Joe Biden said late Monday that he asked his team to develop appropriate options to hold accountable those responsible, in close coordination with the European Union, other allies and partners, and global organizations.
The 30-nation military organization's ambassadors are meeting later Tuesday and will discuss the episode.
Britain's Foreign Secretary Dominic Raab said the interception was a "shocking assault on civil aviation".
"It's very hard to believe that this kind of action could have been taken without at least the acquiescence of the authorities in Moscow", he told parliament.
Russia's foreign ministry said Sapega may also face criminal charges.
Belarusian authorities had diverted the flight as it passed over the country because of a suspected bomb alert, state news agency BelTA said.