HAVANA - A power outage knocked out electricity across several provinces in eastern Cuba early Thursday, from central Ciego de Avila to eastern Guantanamo, according to the state-run National Electric Union (UNE).

The outage occurred after Granma province in eastern Cuba lost power Wednesday night following a sudden drop in frequency on one of the main transmission lines.

Power is "in the process of being restored," the UNE said Thursday, without specifying how long it would take to fully restore service.

Cuba's Minister of Energy and Mines, Vicente de la O Levy, said Wednesday that Cuba's power failures are "primarily due to the strict energy embargo." Hours earlier, Cuban President Miguel Diaz-Canel described the energy crisis as "particularly tense" after the oil supplies delivered by a Russian ship in late March were depleted.