ENTEBBE, Uganda—The government of Venezuelan President Nicolás Maduro is selling off his country’s gold reserves. Some of it has passed through a secretive operation in East Africa, a gambit that evades U.S. sanctions.

On two early-March flights, at least 7.4 tons of gold with a market value over $300 million moved from Venezuela to a refinery in Uganda, say officials in Venezuela and Uganda, a foreign diplomat and Venezuelan opposition lawmakers, who have concluded Mr. Maduro’s government exported the ingots.

The...