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.

Electricity had been restored to most of Spain and Portugal early on Tuesday after huge nationwide blackouts, although authorities were still trying to find out what caused the sudden outage.