MOSCOW — Belarus' isolation deepened Tuesday as commercial planes avoided its airspace, the European Union worked up new sanctions, and a senior U.N. official said he was concerned for the welfare of an opposition journalist arrested in Minsk after his plane was diverted there, apparently on the orders of the country's longtime strongman.

After his detention, Raman Pratasevich was seen in a brief video clip shown on Belarusian state television late Monday, speaking rapidly to say that he was confessing to some of the charges authorities have leveled against him. The spokesperson for the U.N.'s human rights office, Rupert Colville, said Pratasevich's appearance was likely not voluntary and that he seemed to have bruising to his face, though it was difficult to tell from the footage.

The 26-year-old journalist and activist was arrested Sunday after Belarusian flight controllers told the crew of a Ryanair jetliner he was aboard that there was a bomb threat against the flight and ordered it to land. A Belarusian MiG-29 fighter jet was scrambled to escort the plane in a brazen move by President Alexander Lukashenko, who has ruled the country with an iron fist for over a quarter-century.

The diversion and arrest elicited widespread shock and fury, and EU leaders took unusually swift action in response at a summit Monday. They agreed to ban Belarusian airlines from using the airspace and airports of the 27-nation bloc, imposed sanctions on officials linked to Sunday's flight diversion, and urged the International Civil Aviation Organization to start an investigation into the episode some described as state terrorism or piracy. 

They demanded Pratasevich's release and urged European carriers to avoid Belarus' airspace. Polish carrier LOT and Baltic airlines have begun bypassing Belarus. Air France, KLM, Finnair, Lufthansa and Austrian Airlines have all said they will also avoid flights over the country. The U.K., which is no longer part of the EU, also recommended that carriers don't fly over Belarus, and British Airways flights were avoiding the country.

Belarus has defended its actions and its Transport Ministry said Tuesday that it has invited representatives of the international aviation organization and U.S. and EU authorities to investigate the flight's diversion.

In a sign that tensions remained high, NATO Secretary-General Jens Stoltenberg described the Ryanair flight's diversion as "dangerous and unacceptable" and welcomed the EU response. "This is a state hijacking and demonstrates how the regime in Minsk attacks basic democratic rights and cracks down on freedom of expression and independent media," Stoltenberg said. 

The 30-nation military organization's ambassadors are meeting later Tuesday and will discuss the episode. 

Pratasevich, who was arrested along with his Russian girlfriend, Sofia Sapega, was later seen in a brief video clip shown on Belarusian state television, saying he was giving evidence to investigators about his organization of mass disturbances.

Colville, the U.N.'s human rights office spokesperson, denounced the plane's diversion as "abuse of state power" that deserves "the strongest condemnation." He said that Pratasevich's brief appearance on Belarus state television Monday night "was not reassuring, given the apparent bruising to his face, and the strong likelihood that his appearance was not voluntary and his 'confession' to serious crimes was forced."

"This astonishing episode constitutes a new phase in the Belarusian authorities campaign of repression against journalists and civil society in general," Colville said. 

Pratasevich, who left Belarus in 2019 and ran a popular messaging app that played a key role in helping organize huge protests against Lukashenko, has been charged in absentia with staging mass riots and fanning social hatred. Those charges carry a prison sentence of up to 15 years. 

The Telegram messaging app's Nexta channel that he co-founded has been labeled "extremist" by the Belarusian authorities, and some fear Pratasevich could face more serious charges, including some that carry the death penalty.

Speaking to The Associated Press in Warsaw, Stsiapan Putsila, another Nexta co-founder, said he and his colleagues have received "thousands of threats" in the past to blow up their office in the Polish capital. He added that following Pratasevich's arrest, they have received a flow of new threats "that we are the next, that we will not be even taken to Belarus but will be executed right away, that our office will be blown up and we have to be afraid."

Putsila said that the group relies on police protection and undertake "all the possible safety measures to minimize threats and carry out our everyday work."

Belarus has been rocked by months of protests, which were triggered by Lukashenko's reelection to a sixth term in an August 2020 vote that the opposition rejected as rigged. More than 34,000 people have been arrested in Belarus since then, and thousands beaten.

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 international organizations.

"This outrageous incident and the video Mr. Pratasevich appears to have made under duress are shameful assaults on both political dissent and the freedom of the press," Biden's statement said.