ATHENS, Greece (AP) — Greece’s government on Monday said that a major radio communications failure that shut the country’s airspace a day earlier is unlikely to have been a cyberattack, though the cause remains under investigation.

Flights across Greece were grounded, diverted or delayed for several hours Sunday after noise was reported on multiple air traffic communication channels.

“There is not the slightest indication that we are dealing with a cyberattack,” government spokesman Pavlos Marinakis said. “I need to make that clear.”

The Greek Civil Aviation Authority said that noise across all channels, including backup systems, triggered the shutdown, which lasted several hours before operations were gradually restored.

Incoming flights were diverted to several countries in the region, creating a large backlog and leaving thousands of passengers stranded.

The Brussels-based European Organization for the Safety of Air Navigation, widely known as Eurocontrol, assisted in redirecting flights during and following the outage and said that about 120 flights were grounded Sunday at Greece’s two largest airports in Athens and Thessaloniki.

The impact from the disruption lasted through early Monday, the agency said.

Greece’s Air Traffic Controllers’ Association said the outage underscored its long-standing calls to modernize and replace outdated equipment.

A judicial inquiry and an internal investigation were launched Monday into the cause of the outage.

Separately, Transport and Infrastructure Minister Christos Dimas announced the formation of an investigative committee that includes representatives from civil aviation authorities, the Greek air force, Eurocontrol and a Greek state-run cyberdefence agency.

The minister described Sunday’s disruption as “a very serious incident,” but stressed that passenger safety was never at risk.