The country’s top officials were trying to determine the cause of an outage that left tens of millions of people across the Iberian Peninsula without power.

A cross-border power blackout on Monday paralysed the Iberian Peninsula for most of the day, disrupting millions of lives across Spain and Portugal – even interrupting the French electrical system. The sweeping power outage that hit Spain and Portugal this week has raised questions about the electricity grid in a region not normally known for blackouts.

General power outages, such as the one that struck Spain and Portugal earlier this week, can stem from various causes, but the incident underscored