MOSCOW — The strongman president of Belarus sent a fighter jet to intercept a European airliner traveling through the country’s airspace on Sunday and ordered the plane to land in the capital, Minsk, where a prominent opposition journalist aboard was then seized, provoking international outrage.

The stunning gambit by Aleksandr G. Lukashenko, a brutal and erratic leader who has clung to power despite huge protests against his government last year, was condemned by European officials, who compared it to hijacking. It underscored that with the support of President Vladimir V. Putin of Russia, Mr. Lukashenko is prepared to go to extraordinary lengths to repress dissent.

The Ryanair flight from Athens to Vilnius, Lithuania, carrying some 170 passengers — among them the journalist, Roman Protasevich — was flying over Belarus when Belarusian air traffic controllers notified its pilots of “a potential security threat on board” and directed the plane to divert to Minsk, the Ireland-based airline said in a statement.