A widespread and unexplained power outage knocked out electricity in most of Spain and Portugal on Monday, shutting off traffic lights and causing chaos at airports, train stations and on the roads.

A countrywide power outage impacted Spain—as well as swaths of Portugal and smaller portions of France—Monday afternoon, affecting essential services and wreaking chaos across the Iberian Peninsula. The cause of the outage is currently being investigated by Spanish and Portuguese officials and ministers.

Some 96 departing flights from Portuguese airports have been grounded so far, while 45 have been called off from Spain.