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By Tim Hepher
PARIS, May 23 (Reuters) - The United Nations' aviation agency said it was "strongly concerned" by the apparent forced landing of a Ryanair jetliner in Belarus, as global airlines called for an investigation into Sunday's rare incident.
Aviation leaders reacted with shock after Belarus scrambled a fighter and flagged what turned out to be a false bomb alert to force a Ryanair jet to land, before detaining an opposition-minded journalist who had been on board.
The UN's International Civil Aviation Organization (ICAO) said the incident may have contravened a core aviation treaty, part of the international order created after World War Two.
"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," it said.
"We look forward to more information being officially confirmed by the countries and operators concerned."
Airlines joined a flurry of government protests.
"We strongly condemn any interference or requirement for landing of civil aviation operations that is inconsistent with the rules of international law," said the International Air Transport Association.
"A full investigation by competent international authorities is needed."
Aviation experts said the rare incident could fuel debate over the resilience of a decades-old system of cooperation.
ICAO has no regulatory power, but sits at the centre of a system of safety and security standards that keep most airways open across political barriers. These are managed through the Montreal agency by its 193 member states, including Belarus.
"It looks like a gross abuse of the (Chicago) Convention. It's piracy," Kevin Humphreys, a former Irish aviation regulator, told Reuters.
He added he would "not be surprised" if some airlines skirted Belarus airspace while they awaited more details, but stressed each would make its own threat assessment.
"People in the industry will be worried," he added.
Belarus is an important corridor between Europe and Moscow or southeast Asia and Europe, according to Flightradar 24.
Lawyers say Sunday's flight was emblematic of a tangle of jurisdictions that share a delicate co-existence in aviation - involving a Polish-registered jet flown by an Irish group between EU nations Greece and Lithuania, over non-EU Belarus.
Under the 1944 Chicago Convention, each country has sovereignty over its own airspace, though the treaty prohibits any use of civil aviation that may endanger safety.
But the right to overfly other countries is enshrined in a side treaty called the International Air Services Transit Agreement, of which Belarus is not listed as a member. Non-treaty members grant overflights according to varying rules.
A separate 1971 treaty that includes Belarus outlaws the seizure of aircraft or knowingly communicating false information in a way that endangers aircraft safety.
The European Union Aviation Safety Agency (EASA) said it was "monitoring the situation from the safety perspective."
It is not the first time an abrupt diversion has fuelled diplomatic tensions, but the first in memory that a commercial flight governed by civil treaties is involved, Humphreys said.
In 2013, Bolivia said President Evo Morales' plane had been diverted on a flight from Russia and forced to land in Austria over suspicions - later denied - that former U.S. spy agency contractor Edward Snowden, wanted by Washington for divulging secret details of U.S. surveillance activities, was on board. (Reporting by Tim Hepher; Additional reporting by Laurence Frost; Editing by Alexander Smith, Timothy Heritage and Diane Craft)
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