MEDELLÍN, Colombia — United States officials have accused President Nicolás Maduro of Venezuela of a corruption scheme in which his officials, family members and business partners made off with large sums of money meant to feed the country’s starving population.

The allegations appeared Thursday in a new round of sanctions targeting three stepsons of Mr. Maduro and a Colombian business partner of theirs named Alex Saab, among others. American officials said that for years the men had used shell companies and no-bid contracts to siphon off government money, largely from Venezuela’s state-run food program, for their own profit.

“Alex Saab engaged with Maduro insiders to run a wide-scale corruption network they callously used to exploit Venezuela’s starving population,” United States Treasury Secretary Steven Mnuchin said in a statement.

He added: “They use food as a form of social control, to reward political supporters and punish opponents, all the while pocketing hundreds of millions of dollars through a number of fraudulent schemes.”