Monday’s nationwide outage was the third this year and comes on top of state-imposed rolling electricity cuts aimed at conserving the little remaining fuel.
Some rural areas are plunged into darkness for up to 70 hours at a time, while urban areas have seen planned outages of up to 30 hours.
The state electricity company did not say what had caused this latest unplanned incident.
The country’s second-largest city, Santiago de Cuba, was among places where power had not yet been restored on Tuesday evening local time.
Cuban President Miguel Díaz-Canel has acknowledged the spreading discontent among Cubans.
“There are shortages of transport, food, medicines, there are lengthy power cuts lasting more than 20 hours, that causes dissatisfaction, nobody can be happy, the people are suffering,” he told reporters from Claridad, a Spanish-language weekly newspaper based in San Juan, Puerto Rico.
But he urged Cubans to direct their anger towards the US government instead of his, adding: “People bang pots, some with more anger than others. I say: direct your pot-banging towards our northern neighbours, who are the ones behind these power cuts.”
The US Ambassador to the United Nations, Michael Waltz, however, placed the blame squarely with the Cuban government.
Speaking at a meeting of the UN General Assembly on Tuesday, he urged it to “change your ways and turn the lights back on for your people”.
He added that “there always seems to be enough power for the Cuban dictatorship”.
But Cuba’s foreign minister, Bruno Rodríguez, accused the US of waging “multi-dimensional, non-conventional warfare” against Cuba, which he said had “become ever more cruel” over the last seven months.
US-Cuban relations, which have been strained for decades, have deteriorated rapidly since the start of the year, when US President Donald Trump accused the island’s government of posing a threat to the national security of the US.
Shortly after US forces seized former Venezuelan President Nicolás Maduro – a close ally of the Cuban government – in January, Trump also openly mused that Cuba was “ready to fall”.
Since then, the Trump administration has imposed fresh sanctions on Cuba as well as an effective blockade on oil shipments to Cuba, threatening to slap tariffs on countries which provide it with fuel.
The US has also levelled murder charges against Cuba’s former president, Raúl Castro, who remains an influential figure on the island despite being 95 years old.
Despite trading barbs publicly, the two countries have been holding talks over recent weeks in private.
The Cuban foreign minister said on Tuesday that those talks “show no progress”, but left the door open “to dialogue based on mutual respect and non-interference in Cuba’s internal affairs”.
