The Trump administration increased pressure on Venezuelan President Nicolás Maduro Thursday, targeting a lifeline he's used for selling crude oil run by a close associate of the socialist leader who was recently jailed in Cape Verde.

Focusing primarily on Mexico-based individuals, U.S. Treasury officials sanctioned three people and the companies they ran. They're all now blocked from doing any business with the United States or American citizens.

The stiff financial move is designed to cut off Maduro's government from hard cash earned from oil sales in a campaign led by the United States aimed at ending his rule and the nation's historic political and economic crisis.

“The illegitimate Maduro regime created a secret network to evade sanctions, which Treasury has now exposed,” said Deputy Secretary Justin G. Muzinich said in a statement. “The United States will continue to relentlessly pursue sanctions evaders, who plunder Venezuela’s resources for personal gain at the expense of the Venezuelan people.”

The financial measures don't directly hit Maduro ally and Colombian citizen, Alex Saab, who has already been indicted by U.S. officials and arrested in recent days. But officials say they net Saab's associates, who are accused of working to help Venezuela's state-owned oil firm PDVSA evade U.S. sanctions.

The fresh sanctions target Saab associate, Joaquin Leal, who is a Mexican national. U.S. officials accuse the two men of selling crude oil from Venezuela under the guise of operating an “oil-for-food” program that never resulted in food deliveries to Venezuela.

Leal worked with Mexico-based companies Libre Abordo and Schlager Business Group — also newly sanctioned — to broker the re-sale of over 30 million barrels of crude oil on behalf of PDVSA. U.S. officials that amounted to roughly 40% of PDVSA’s oil exports in April.

Olga Maria Zepeda and her mother Veronica Esparza were sanctioned as co-owners of the two firms, officials said.

Schlager Business Group, which had no prior experience in the oil sector, was primarily involved in business administrative and back-office support services, officials said.

It was targeted for allegedly operating in the global oil world on Venezuelan’s behalf by providing financial and technological support for PDVSA, U.S. officials said.

Libre Abordo is a Mexico City-based firm that sold cleaning supplies, hospital equipment and agricultural products. It claimed it went bankrupt in May, but Treasury officials say that in fact it re-sold over 30 million barrels of Venezuelan crude oil. The firm had no prior experience in oil sector before signing a deal with PDVSA, officials said.

In July 2019, however, it signed two contracts with a Venezuelan-controlled firms to supply corn and tanker trucks to Venezuela. Instead of taking the firm’s corn and trucks, Libre Abordo accepted payment in Venezuelan crude oil in a scheme U.S. officials said was orchestrated by Saab and high-ranking Venezuelan official Tarek El Aissami.

Saab was indicted last year by federal prosecutors in Miami on money laundering charges connected to an alleged bribery scheme that pocketed more than $350 million from a low-income housing project for the Venezuelan government that was never built. In private, U.S. officials describe Saab as a frontman for Maduro.

Saab was arrested Friday while en route to Iran in a blow to Maduro’s government. U.S. officials believe he holds many secrets about how Venezuela's leader, his family and top aides allegedly siphoned off millions of dollars in government contracts amid widespread hunger in the oil-rich nation.

It was unclear how American authorities, who had been targeting the Colombian businessman for years, finally caught up with him. Saab remains in custody on the West African island, and his attorney has said he intends to fight extradition to the U.S.