Cuba has completely run out of diesel and fuel oil, the country's Energy Minister Vicente de la O Levy has said.
In an interview with state-run media, de la O Levy said there were limited amounts of gas available, but that Cuba's energy system was in a "critical" state as a US-led blockade of oil to the country squeezed supply.
Scattered protests against power cuts broke out in the capital Havana on Wednesday, the Reuters news agency reported.
The US this week reiterated its offer of sending $100m (£74m) in aid to the country in exchange for "meaningful reforms to Cuba's communist system".
"The sum of the different types of fuel: crude oil, fuel oil, of which we have absolutely none; diesel, of which we have absolutely none - I am being repetitive - the only thing we have is gas from our wells, where production has grown," de la O Levy said.
Under the US blockade, parts of Havana have been plunged into 20 to 22-hour blackout periods, he continued.
He also acknowledged that the situation in the country had been "extremely tense".
Hospitals have been unable to function normally, while schools and government offices have been forced to close. Tourism, an economic engine for Cuba, has also been impacted.
Cuba normally relies on Venezuela and Mexico to supply oil to its refinery system. However, the two countries have largely cut off supplies since US President Donald Trump threatened tariffs on countries that send fuel to Cuba.
As the island continues to grapple with these energy shortages, rare protests erupted in Havana on Wednesday evening.
Hundreds of Cubans took to the streets across the city, blocking roads with burning rubbish and shouting anti-government slogans.
It marked the biggest single night of demonstrations in the city since Cuba's energy crisis began in January, Reuters reported.
Residents of the San Miguel del Padron neighbourhood could be heard shouting "turn on the lights!", the AFP news agency said.
Taking to social media on Wednesday, Cuban President Miguel Diaz-Canel blamed the US for the energy shortages as he acknowledged the "particularly tense" situation across the island.
"This dramatic worsening has a single cause: the genocidal energy blockade to which the United States subjects our country, threatening irrational tariffs against any nation that supplies us with fuel," he wrote.
Last week, US Secretary of State Marco Rubio said Havana had rejected a US offer of humanitarian aid worth $100m (£74m), a claim Cuba denied.
The US State Department repeated its offer on Wednesday, saying the humanitarian assistance would be distributed in coordination with the Catholic Church and "reliable" humanitarian organisations.
It continued: "The decision rests with the Cuban regime to accept our offer of assistance or deny critical living-saving aid and ultimately be accountable to the Cuban people for standing in the way of critical assistance."
Washington's blockade on the country ramped up in early May when the US targeted senior Cuban officials in a wave of sanctions accusing them of committing "human rights abuses".
Cuban Foreign Minister Bruno Rodriguez called the sanctions "illegal and abusive".
