The cause of Spain and Portugal’s widespread blackouts remained a mystery on Tuesday, with some isolated disruption remaining after power was largely restored to both countries.

That conclusion has been supported by the operator of Spain’s national grid, Red Eléctrica, which has located where outages began on Monday. Two separate incidents of power outages led to instability in the grid leading to a “breakdown in interconnections with France,” leaving the Iberian grid isolated.

A widespread power outage hit Spain and Portugal, affecting millions of people who live across Europe's Iberian Peninsula.