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.

BARCELONA, Spain (AP) — A major power outage hit Spain and Portugal on Monday, including their capitals, knocking out subway networks, phone lines, traffic lights and ATM machines. It is rare to have such a widespread outage there. Spanish generator Red Eléctrica said it affected the Iberian peninsula and the incident is being assessed.

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.