By Tim Hepher

The International Civil Aviation Organization said the incident may have contravened the Chicago Convention, a 1944 treaty that set rules for the burgeoning industry anticipated after World War Two and which underpins civil aviation today.

Authorities in Belarus scrambled a fighter jet and flagged what turned out to be a false bomb alert to force a Ryanair plane to land, drawing international criticism.

The jet was flying through Belarus airspace en route from Athens to Lithuania when it was diverted to Minsk, the capital of Belarus, where authorities detained an opposition-minded journalist who had been on board.

“ICAO is strongly concerned by the apparent forced landing of a Ryanair flight and its passengers, which could be in contravention of the Chicago Convention,” the agency said in a Twitter post.

“We look forward to more information being officially confirmed by the countries and operators concerned”.

ICAO has no regulatory power, but sits at the centre of a system of safety and security standards that are managed through the Montreal agency by its 193 member states, including Belarus.

Aviation experts said the incident could fuel debate over the resilience of a decades-old system of cooperation.

Under the landmark 1994 Chicago Convention, each country has complete sovereignty over its own airspace, though the treaty prohibits any use of civil aviation that may endanger safety.

A separate 1971 treaty signed in Montreal, of which Belarus subsequently became a member, outlaws the seizure of aircraft and various offences including knowingly communicating false information in a way that endangers aircraft safety. (Reporting by Tim Hepher; Editing by Alexander Smith and Timothy Heritage)