British Airways has canceled all flights out of London’s Heathrow and Gatwick airports on Saturday following a “major IT system failure” that wreaked havoc at airports worldwide. The global computer outage, which the airline said it does not think is a cyberattack, struck on a major holiday weekend, leaving thousands of travelers stranded. Delays have also been reported in Rome, Prague, Milan, Stockholm and Malaga, the BBC reported. The airline has not provided any further details on what is causing the system failure but urged passengers against going to the airports. The airline’s call centers and website were also affected by the malfunction. “It's frozen the whole system so no British Airways plane can actually take off, they can't move the baggage, they can't issue passenger credentials, in fact they cant do anything at all,” aviation expert Julian Bray was cited as saying by the BBC. All passengers affected have been offered the chance to get a refund or reschedule their flights. The airline warned that the disruptions could continue into Sunday but promised it was working to fix the situation as quickly as it could. “We apologize for the current IT systems outage. We are working to resolve the problem as quickly as possible,” the airline said on Twitter.