A Ryanair plane flying from Greece to Lithuania has been diverted to Minsk, with Belarusian opposition figures saying it was done so a journalist on board could be arrested.
The opposition Nexta channel on Telegram said its ex-editor Roman Protasevich had been detained.
Svetlana Tikhanovskaya, beaten by Alexander Lukashenko last year in polls widely denounced as rigged and now living in exile, demanded his release.
Belarus has not officially commented.
Since August's election the 66-year-old Mr Lukashenko, who has ruled the country since 1994, has cracked down on dissenting voices, with many opposition figures either arrested or fleeing abroad.
Lithuanian President Gitanas Nauseda tweeted that Belarus was behind an "abhorrent action"
The diversion of Flight FR4978 from Athens to Vilnius on Sunday was carried on the flightradar124 website, showing the plane turning east to Minsk shortly before it reached the Lithuania border. Ryanair has not yet responded to a request for comments.
Russian media quoted the Minsk airport press service as saying the plane had made an emergency landing following a bomb scare.
Belta, the state-owned news agency in Belarus, said Mr Lukashenko had given the order for the plane to land at Minsk and that a MiG-29 fighter jet had been despatched to accompany the Ryanair plane.
Nexta said no bomb was found on board and the passengers were searched, after which Mr Protasevich, 26, was detained.
In a series of tweets, Ms Tikhanovskaya accused the Belarus government of forcing the plane to land to arrest Mr Protasevich, who she said faced the death penalty as he has been categorised as a terrorist.
She said Mr Protasevich had left Belarus in 2019 and covered the events of the 2020 presidential election with Nexta, after which criminal charges were filed against him in Belarus.
Western leaders have backed Ms Tikhanovskaya, who claimed victory in the election before she was forced to leave Belarus for Lithuania. She had become a candidate after her husband was jailed and barred from running.
Tens of thousands of protesters thronged the capital Minsk for months last year, furious at Mr Lukashenko's declaration of victory. There have been numerous cases of police brutality and some 2,700 prosecutions this year alone.
