But in the short run, they are meant to end the arrangement by which the Maduro government provides oil to Cuba in exchange for intelligence and counterintelligence services while the Venezuelan people lack food, medicine and clean water. Venezuela has been shipping 20,000 to 50,000 barrels of oil a day to Cuba, according to experts in the oil industry and administration officials.

Russ Dallen, the managing partner of Caracas Capital Markets, who specializes in the Venezuelan oil industry, said the most likely outcome of the sanctions would be to create an atmosphere in which shipping companies would be even more wary of doing business with either Cuba or Venezuela, for fear of triggering sanctions.

He said they were also meant to “name and shame” companies that have transported Venezuelan oil to Cuba so that Mr. Maduro can help an ideological ally rather than use profits from the oil to feed a starving population.

“It makes Cuba and Venezuela even more radioactive,” he said.

Mr. Dallen, who tracks oil shipments leaving Venezuela, said that some of the ships had begun turning off their transponders when in Venezuelan ports, something regulations prohibit but is a technique used in countries like Iran to conceal their presence in the country. One ship, Mr. Dallen said, had recently left its transponder off until it reached Europe.

The sanctions come as Venezuela has faced a month of blackouts that have resulted in an estimated loss of a week’s oil production.