Grid operator UNE said on social media it is investigating the causes of the blackout on Monday, the latest in a series of widespread outages that last for hours or days and that this weekend sparked a rare violent protest in the communist-run country.
The United States has ratcheted up pressure this year on long-time foe Cuba since capturing Venezuelan President Nicolas Maduro - Cuba's most important foreign benefactor - in January.
US President Donald Trump cut off Venezuelan oil shipments to Cuba and threatened to slap tariffs on any country that sells oil to Cuba, strangling the Caribbean island's already antiquated grid.
Cuba said on Friday that it had entered into talks with the United States with the hope of defusing the crisis. Trump has said in recent weeks that Cuba is on the verge of collapse and is eager to make a deal with the US.
The Ministry of Energy and Mines on X noted a "complete disconnection" of the country's electrical system on Monday and said it was investigating, noting there were no failures in the units that were operating when the grid collapsed.
It was the third major blackout in Cuba over the past four months.
Cuba has received only two small vessels carrying oil imports this year, according to LSEG ship tracking data seen by Reuters on Monday.
The first tanker discharged fuel in January at the Havana port coming from Mexico, which was a regular supplier to the island until then. The second vessel, from Jamaica, discharged liquefied petroleum gas - known as cooking gas - in February.
Venezuela, once Cuba's main oil supplier, has sent no fuel to the island this year.
Venezuela's state company PDVSA last month loaded gasoline in a tanker that it had previously used to transport fuel to Cuba, but the vessel has not left Venezuelan waters, PDVSA documents and tanker monitoring data showed.
No large imports have entered this year through Cuba's main hubs of Matanzas or Moa, which typically handle crude for refining and fuel oil for power generation, according to satellite images analyzed by TankerTrackers.com.
The ports of Havana and Cienfuegos also have not had import activity in more than a month, it added.
with AP
