Spain’s top security and defense officials were meeting on Wednesday morning to discuss the blackout on the Iberian Peninsula this week, which halted critical infrastructure for up to 18 hours in some areas.

The authorities in Spain and Portugal are under pressure to figure out what caused the power grid to shut down. The Spanish government has asked European regulators and various domestic agencies to investigate what happened.

Spain’s National Security Council convened in Madrid at 9 a.m. local time to discuss the blackout. Prime Minister Pedro Sánchez, the chief of his Defense Staff and the directors of the country’s National Intelligence Center and Department of National Security were expected to attend.