New Delhi, Jan. 6 -- 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 flig...