Airlines are shunning Belarus's air space and Belarusian planes could soon be banned from Europe, potentially isolating the country apart from its border with Russia after it forced down a jetliner and arrested a dissident journalist.
A video released overnight showed 26-year-old Roman Protasevich confessing to having organised anti-government demonstrations.
On Sunday he was pulled off the passenger plane that was forced to land in the Belarusian capital Minsk.
Exiled opposition leader Sviatlana Tsikhanouskaya said the video left no doubt that Protasevich had been tortured.
"He said that he was treated lawfully, but he's clearly beaten and under pressure. There is no doubt that he was tortured. He was taken hostage," she told a news conference in the Lithuanian capital Vilnius on Tuesday.
Protasevich and a 23-year-old student travelling with him were arrested after their Ryanair flight was escorted by a Belarusian warplane while flying from Greece to Lithuania.
Western powers have widely condemned the incident, which NATO Secretary-General Jens Stoltenberg described on Tuesday as a "state hijacking".
Belarusian state media have reported that President Alexander Lukashenko personally ordered the flight to be intercepted.
Belarus says it was responding to a bomb scare that later proved to be a false alarm.
The UN agency ICAO has said the incident may have violated the foundational treaty governing international civil aviation, the 1944 Chicago Convention.
At least three other people disembarked the flight in Minsk, assumed by Western countries to have been spies who had helped coordinate an operation to capture Protasevich.
One Lithuanian official told Reuters that the three passengers who disembarked included two Belarusian citizens and one Greek citizen. Belarusian state TV on Monday broadcast interviews with the trio.
European Union leaders at a summit on Monday called for airlines based in the 27-member bloc to halt flights over Belarusian air space, which is along a major corridor connecting Europe and Asia and earns hard currency from overflight rights.
Lufthansa, KLM, SAS, Air France, LOT and Singapore Airlines were among carriers that announced they would stop flying over Belarus.
The EU leaders also directed officials to draw up unspecified new sanctions against Belarus, and to work out a way to ban Belarusian airlines from the bloc's skies.
If all such measures are fully implemented, flights may soon be able to reach Belarus only by passing over its eastern border with its close ally Russia.
Lukashenko, whose security services crushed months of pro-democracy demonstrations last year after an election opponents said was rigged, has so far shrugged off Western sanctions, which mostly consist of blacklists barring various officials from travelling or doing business in the United States and EU.
Politicians in the West have called for tougher measures that might isolate the country from the international financial system or bar its exports. But they have failed to influence the behaviour of Lukashenko, who enjoys unwavering financial and security support from Russia, which considers the Belarusian frontier with NATO its first line of defence.
Russia has denied involvement in the plane incident and has accused Western countries of hypocrisy, noting that a Bolivian presidential plane was diverted to Austria in 2013 after reports it was carrying US intelligence leaker Edward Snowden.
In the video released overnight, Protasevich can be seen seated at a desk in a dark hooded sweatshirt.
"I can state that I don't have any health issues, including diseases of the heart or any other organs. Police officers are treating me properly and according to the law," he says. "Also, I now continue to cooperate with the investigation and have confessed to organising mass protests in Minsk."