Sri Lanka, Jan. 4 -- Thousands of passengers are stranded across Europe after a communications failure forced Greece to close its airspace, causing widespread cancellations and delays.

Officials are working to understand why radio communications were disrupted on Sunday morning, prompting the temporary suspension of arrivals and departures.

Some departures have since been allowed to resume - though inbound flights are still being told to divert or return to their point of origin. Athens' main airport is among the worst affected, while Thessaloniki airport has closed entirely.

The timing of the disruption has raised fears that travellers will not be able to get home before the start of the working week.

"I was supposed to fly to London...