Power began returning to households in Spain and neighbouring Portugal, hours after cities across the Iberian Peninsula were plunged into darkness in one of Europe's most severe blackouts.Investigators are still looking into the cause of the blackout which remains unclear,

Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

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