Belarusian President Alexander Lukashenko said Wednesday he had acted "lawfully to protect people" by diverting a Ryanair flight over Belarusian airspace, an act that sparked a global outcry.

The Athens-to-Vilnius flight carrying a wanted opposition activist was forced to make a landing in Minsk on Sunday over a supposed bomb scare, prompting several EU carriers to stop flights over Belarus.

"I acted lawfully to protect our people," Lukashenko said in an address to members of parliament, the Belta state-run news agency reported.

The strongman leader, who has ruled over the ex-Soviet nation for over two decades, also said "attacks" on his country had crossed "red lines".

"As we predicted, our ill-wishers at home and abroad have changed their methods of attacking the state," Lukashenko said.

"They have crossed many red lines and crossed boundaries of common sense and human morality."

Lukashenko added it was an "absolute lie" that a Mig-29 fighter jet forced the flight to land in Minsk.

Lukashenko and his allies are under European and US sanctions over the violent crackdown on post-election protests that gripped the nation last year.

Tens of thousands took to the streets to demand the resignation of 66-year-old Lukashenko, saying his election challenger Svetlana Tikhanovskaya was the true winner of the vote.

Tikhanovskaya fled to EU member Lithuania shortly after the election.

The European Union said it was eyeing fresh sanctions on Lukashenko's regime after the plane incident.

European leaders have also demanded the release of Roman Protasevich, the opposition activist who was on board the plane and arrested by Belarus authorities in Minsk.

The 26-year-old activist co-ran the Nexta Telegram channels, prominent voices of the opposition that helped mobilise and coordinate protesters.

He faced up to 15 years of jail on charges of organising mass unrest.