The European Union has agreed to ban airlines in Belarus from using EU airspace, after Belarusian authorities forced a passenger plane to make an unscheduled landing. Dissident journalist Roman Protasevich was subsequently arrested.
EU leaders condemned the incident in their meeting on Monday and called for his immediate release.
Protasevich was taken into custody on Sunday after his plane was ordered to land in the Belarusian capital of Minsk while it was crossing through the country's airspace.
The EU leaders agreed to sanction Belarus by denying its airlines access to EU airspace and airports. They also urged EU-based carriers to avoid flying over Belarus.
Belarusian authorities have defended their action, saying they had received a bomb threat from the Palestinian militant group Hamas and the landing was necessary for security reasons.
No explosives were found on the Ryanair plane, which was flying from Greece to Lithuania.
A United Nations spokesperson said on Monday that Secretary-General Antonio Guterres is deeply concerned, and "supports calls for a full, transparent and independent investigation into this disturbing incident, and urges all relevant actors to cooperate."
The spokesperson said Guterres also remains "greatly concerned by the deteriorating human rights situation in Belarus" following the presidential election last August that saw Alexander Lukashenko re-elected to a sixth term.
The spokesperson said Guterres urges the Belarusian authorities to "fully respect all its international human rights obligations," including freedoms of expression and assembly.
The International Civil Aviation Organization says the President of its Council of 36 member states has called an urgent meeting to discuss the incident. EU leaders have urged ICAO, a UN body, to launch an emergency investigation.