A Russian tanker full of oil is moving through the Atlantic Ocean and drawing scrutiny to see if it is heading to Cuba, a potential test of the U.S. oil blockade of the island, according to shipping data and industry analysts.

The ultimate destination of the tanker is still unknown. But if Russia is attempting to send oil to Cuba, as some analysts suspect, it could represent a critical lifeline for the Cuban government — and a new potential showdown between two superpowers over the small island nation.

Cuba has not received a significant shipment of fuel since Jan. 9, soon after the United States captured Venezuela’s president and took control of its oil exports, which once largely powered Cuba.

That is causing a severe crisis for Cuba. The Trump administration has threatened other nations not to send fuel, hoping to choke Cuba’s government into submission.

The tanker, called the Anatoly Kolodkin and owned by the Russian government, is carrying an estimated 730,000 barrels of crude oil, which analysts estimate could buy Cuba weeks of energy.

The ship exited the English Channel into the northern Atlantic this week and could reach the Caribbean as early as Monday, according to ship data analyzed by Kpler, a shipping data firm.

The Anatoly Kolodkin left Primorsk, Russia, on the Baltic Sea on March 9, according to Kpler data, and publicly broadcast its destination as “Atlantis, USA,” a possible ruse. In 2024, the U.S. government placed sanctions on the tanker and its owner, a Russian state-owned shipping company called Sovcomflot, meaning that it would be highly unlikely for it to dock in the United States. Kpler reported that its actual destination is Matanzas, Cuba, citing an industry insider.

The tanker transited the English Channel escorted by a Russian naval ship, but its naval escort turned back once the tanker entered the Atlantic, according to the British Navy.

The Anatoly Kolodkin would not be the first tanker to attempt to bring Russian fuel to Cuba in recent weeks.

The Sea Horse, a tanker loaded with nearly 200,000 barrels of gas oil believed to be from Russia, had been headed to Cuba when it abruptly stopped in the middle of the Atlantic last month, according to ship-tracking data and a person familiar with the tanker’s operations who was not authorized to speak publicly.

The Sea Horse, which is owned by a Chinese firm, halted its shipment because its owners feared consequences from the U.S. government if they delivered fuel to Cuba, the person said. That decision, which has not been previously reported, came as President Trump continued his threats against the island nation and those who delivered oil to it.

Analysts were puzzled when the tanker then spent the next three weeks drifting in the Atlantic. On Tuesday, the Sea Horse set course for another Caribbean destination and is now seeking a new buyer for its cargo, the person said.

Cuba, Russia and the Anatoly Kolodkin’s owner did not respond to requests for comment.

After 10 weeks of an effective U.S. oil blockade, Cuba’s energy crisis is growing dire, with soaring gas prices, near daily blackouts and a looming humanitarian disaster. Medical care, nutrition, education and sanitation are all rapidly deteriorating. And Cuban officials have warned the nation’s power grid is on the verge of collapse.

The Trump administration is attempting to strangle the Communist government in Cuba into complying with its demands, including that President Miguel Díaz-Canel steps down. The White House has enforced the blockade with threats of tariffs and, in one case, the U.S. military: On Feb. 12, a U.S. Coast Guard vessel escorted a tanker full of Colombian oil to the Dominican Republic after it had previously been en route to Cuba.

Two U.S. Coast Guard Cutters are currently patrolling the waters near Cuba, according to a U.S. official who spoke on the condition of anonymity to discuss operational matters.

“The Coast Guard and our federal partners maintain a continuous presence in the Florida straits and Caribbean,” the Coast Guard said.

Some of the U.S. military fleet that had been stationed in the Caribbean Sea ahead of the U.S. attack on Venezuela has since departed for the Middle East as part of the war in Iran. On Thursday, Gen. Francis L. Donovan, the top general overseeing U.S. forces in Latin America, told Congress that the U.S. military was not rehearsing any plans to overthrow the Cuban government or occupy the nation.

Yet Mr. Trump has been heightening his threats. On Monday, he said that Cuba is so weakened that he believes he will have “the honor of taking Cuba” and that he “could do anything I want with it.”

Mr. Díaz-Canel, Cuba’s president, responded that the U.S. government wants “to take over the country, its resources, its properties, and even the very economy they seek to suffocate in order to force us to surrender.” He added, “Faced with the worst-case scenario, Cuba is guided by one certainty: any external aggressor will face unyielding resistance.”

The morning after Mr. Trump’s comments, Dmitry Peskov, a Kremlin spokesman, told reporters that Russia was in close contact with Cuba about its energy crisis and was “ready to provide all possible assistance.”

He added, “Cuba is an independent sovereign state that faces major economic difficulties due to the suffocating embargo imposed on the country.”

He did not name the United States or Mr. Trump.

The Anatoly Kolodkin — which is named for Russia’s former maritime law representative at the United Nations — could change the trajectory of the Cuban energy crisis.

Its 730,000 barrels of crude oil can produce diesel, gasoline and jet fuel, while also helping to power the electric grid, said Jorge Piñón, a former oil executive who studies Cuba’s energy at the University of Texas.

But if it arrives in Cuba, the crude would first need to be refined. Cuba’s refineries are highly inefficient, Mr. Piñón said, meaning it would likely take several weeks and waste oil.

Cuba needs 100,000 barrels of oil a day to keep its country running, he said. The country is currently surviving on its rapidly dwindling reserves — which may already be empty — and about 40,000 barrels of oil it produces domestically a day, he said.

The Russian oil would be vital, Mr. Piñón said, but only a temporary fix, giving Cuba “breathing room of no more 30 days.”

Note: The International Maritime Organization issues an IMO number, a permanent identification number, that remains associated with a vessel throughout its lifetime, unlike a ship’s name, which can change frequently. The ships in this article are Anatoly Kolodkin (9610808) and Sea Horse (9262584).

Eric Schmitt contributed reporting from Washington, and Anatoly Kurmanaev from London.