Grid operator UNE said on social media it is investigating the causes of the blackout, 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.

Officials ruled out a major power plant failure, but had still not pinpointed the root cause of the grid ​collapse, suggesting a problem with transmission.

Officials said they had begun restoring power to small clusters of ⁠circuits, or microsystems, across the country, an early but necessary first step in bringing the full grid back online.

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 has 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 United States.

Cubans have grown accustomed to power outages, whether tied to the oil supply shortfalls or systemic failures in ‌the grid, ⁠which can also be the result of depressed power generation.

“No, the news didn’t surprise me,” said Havana resident Dayana Machin, 26, adding that all Cubans were scrambling now to find alternatives to grid-provided electricity.

“We’re getting used to living like this.”

RUNNING ON FUMES

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.