British Airways has canceled all flights from London’s Heathrow and Gatwick airports due to a global IT outage Saturday. The airline said they believe the source of the outage was a power supply issue and not a cyber attack.

“We believe the root cause was a power supply issue and we have no evidence of any cyber attack,” British Airways CEO, Alex Cruz, said in a video posted to Twitter.

Heathrow tweeted a statement confirming all BA flights scheduled to take off from London’s two main airports have been cancelled for the rest of Saturday.

UPDATE 2 | All @British_Airways flights leaving from @HeathrowAirport this evening (UTC+1) have been cancelled after a BA IT issue. pic.twitter.com/XzQQaygYtW — Heathrow Airport (@HeathrowAirport) May 27, 2017

We apologise for the current IT systems outage. We are working to resolve the problem as quickly as possible. — British Airways (@British_Airways) May 27, 2017

In an emailed statement to RT, British Airways said:

“Following the major IT system failure experienced earlier today, with regret we have had to cancel all flights leaving from Heathrow and Gatwick for the rest of today, Saturday, May 27."

“We are working hard to get our customers who were due to fly today onto the next available flights over the course of the rest of the weekend. Those unable to fly will be offered a full refund.”

Reports have surfaced of passengers across the world affected by the outage, with delays reported in Rome, Prague, Stockholm, Malaga and Lisbon. Many passengers have criticized the airline for a lack of food and drink provided as a basic means of compensation.

Passengers experiencing delays around the world have vented their frustrations on social media.