After a nearly daylong power outage upended life for millions across Spain and Portugal, the authorities in both countries are still searching for the cause of the disruption.

Some of Spain’s top officials convened on Wednesday morning to discuss the blackout, which halted critical infrastructure starting Monday afternoon for nearly 18 hours in some areas.

Power was almost entirely restored by Tuesday in Spain and Portugal, as well as in southern France, where households in the Basque region were affected.

Spain’s top security and defense officials met on Wednesday to discuss the blackout, with officials saying they were considering a range of possibilities. The Spanish government has asked European regulators and various domestic agencies to investigate what happened.

On Tuesday, Eduardo Prieto, director of services for Spain’s national power company, Red Eléctrica, said that there were no “definitive conclusions” about the reasons for the outage, although he and other officials ruled out a cyberattack.

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