Sanctions have been imposed by the United States on Venezuelan state-owned oil firm PDVSA, White House national security adviser John Bolton declared on January 28.
"We have continued to expose the corruption of (Venezuelan President Nicolas) Maduro and his cronies and today's action ensures they can no longer loot the assets of the Venezuelan people," Bolton told reporters at a briefing on Monday.
Earlier on the same day, Venezuela's opposition leader and self-proclaimed interim president Juan Guaido ordered congress to name new PDVSA boards of directors as well as the U.S. refining subsidiary Citgo.
Guaido's advisers are rushing to take control of Citgo, the country's main foreign asset, before a potential bond default that could leave half the company in creditors' hands, sources close to the talks told Reuters.
Nicolas Maduro is facing an unprecedented challenge to his authority after Guaido declared himself interim president last week, citing a fraudulent election.