The official said he had raised concerns about Heathrow’s electricity supply days before a power outage forced it to shut down. Heathrow disputed the relevance of the official’s comments.

London Heathrow Airport was warned about possible issues with its power supplies a few days before a nearby fire cut electricity to the hub and forced Europe’s busiest airport into an unprecedented day-long blackout.

At least 1,350 flights to and from Heathrow were affected already, including several from US cities that were canceled, flight tracking service FlightRadar 24 said.