Belarus' forced diversion of a plane and arrest of a journalist who was on board has widened a rift between Western powers and Minsk, prompting calls for further sanctions and an international probe over the incident.

Minsk forced the Ryanair flight from Athens, Greece, to Vilnius, Lithuania, to land in Minsk, the Belarusian capital, on Sunday after it scrambled a fighter jet, allegedly in response to a bomb threat.

On its landing, Belarusian authorities took Roman Protasevich, a 26-year-old journalist who has been critical of the government, into custody. His whereabouts remain unknown.

Protasevich is wanted in Belarus on "extremism" charges. He is accused of organising mass riots against the country's longtime President Alexander Lukashenko, as well as inciting social hatred – allegations he denies.

Sunday's incident led to international outrage. Lithuanian President Gitanas Nauseda accused Minsk of undertaking a "state-sponsored terror act" and called for "serious sanctions" against Lukashenko's government, while the EU's executive arm labelled the move a "hijacking".

But Russia, an ally of Lukashenko, accused Western powers of hypocrisy over their remarks.

"It is shocking that the West calls the incident in Belarusian airspace 'shocking'," Foreign Ministry spokeswoman Maria Zakharova wrote on Facebook.

The plane diversion is expected to top the agenda at a two-day summit of EU leaders, who were united in their condemnation of Lukashenko, that began yesterday.

EU foreign policy chief Josep Borrell condemned the "inadmissible step" as "yet another blatant attempt by the Belarusian authorities to silence all opposition voices".

Borrell also indicated toughened EU sanctions against Belarus were incoming, reports Aljazeera online.

The United States and former EU member the United Kingdom called for the immediate release of Protasevich and demanded the council of the International Civil Aviation Organization investigated the incident.

Ryanair Chief Executive Michael O'Leary said Sunday's incident was "state-sponsored piracy".