MOSCOW — The tray tables were being raised and the seat backs returned to their upright positions as passengers on Ryanair Flight 4978 prepared for the scheduled landing in the Lithuanian capital, Vilnius. Then the plane made an abrupt U-turn.

For many passengers, it initially seemed like one of those unexpected delays in airline travel. But after the pilot announced the plane had been diverted to Minsk, the capital of Belarus, one passenger — Roman Protasevich, a prominent Belarusian opposition journalist who had been living in exile since 2019 — grew terrified, certain that he faced arrest.

“He panicked because we were about to land in Minsk,” Marius Rutkauskas, who was sitting one row ahead of Mr. Protasevich, told the Lithuanian broadcaster LRT upon arrival in Vilnius.

Sunday’s ordeal — described by many European officials as an extraordinary, state-sponsored hijacking by Belarus to seize Mr. Protasevich — quickly led to one of the most severe East-West flare-ups in recent years.