A Russian tanker carrying oil to Cuba has entered the waters off the Communist-run island, Russia's Interfax news agency reports.
The oil shipment - the first to reach Cuba since January - comes hours after US President Donald Trump said that he had no problem with countries, including Russia, sending supplies to the island.
Trump's remark appeared to signal a loosening of a de facto oil blockade his administration had imposed on Cuba since January.
Cuba has been experiencing a series of nation-wide blackouts as the blockade exacerbated existing shortages.
According to Interfax, the Russian tanker Anatoly Kolodkin is carrying a "humanitarian shipment" of 100,000 tonnes of crude oil.
Last week, the World Health Organization (WHO) had warned that severe fuel shortages meant that Cuban hospitals were struggling to maintain emergency and intensive care services.
Cuba's situation has deteriorated rapidly since 3 January, when US forces seized Venezuelan leader Nicolás Maduro - a staunch ally of the Cuban government - who had been providing the island with oil under highly preferential terms.
Trump also threatened to impose tariffs on any nation sending oil to Cuba.
Russian Minister of Energy Sergei Tsivilev said on Wednesday that Cuba "had found itself in a difficult situation as a result of sanctions pressure".
"That is why we are currently sending humanitarian supplies to Cuba," he added.
Just over a week ago, the US Treasury department added Cuba to a list of countries barred from receiving oil deliveries from Russia.
But in an apparent reversal of his strategy, Trump told journalists on board of Air Force One on Sunday that he had "no problem" with Russia delivering oil to Cuba.
"We have a tanker out there. We don't mind having somebody get a boatload because they need (...) they have to survive," he said.
It was not clear from Trump's comment if this represented a reversal of the fuel blockade policy or just a temporary softening.
The Russian tanker is expected to offload the oil in Matanzas terminal in the coming hours.
The oil it carries is expected to provide Cuba with a short-term lifeline.
Its Communist government, led by President Miguel Díaz Canel, has been in talks with the Trump administration to find a route out of the crisis.
