Washington (CNN) The United States on Monday sanctioned Venezuela's state-owned oil company, bringing to bear the most significant financial pressure so far on Venezuela's embattled President Nicolas Maduro.

Treasury Secretary Steve Mnuchin and national security adviser John Bolton announced the sanctions against Petroleos de Venezuela, S.A. -- the parent company of the US-based Citgo oil company -- on Monday afternoon from the White House briefing room. The measure blocks about $7 billion in assets and would result in more than $11 billion in lost assets over the next year, Bolton said.

"The United States is holding accountable those responsible for Venezuela's tragic decline," Mnuchin said. "PdVSA has long been a vehicle for embezzlement, for corruption for Venezuelan officials and businessmen. Today's designation of PdVSA will help prevent further diversion of Venezuela's assets by Maduro, and will preserve these assets for the people of Venezuela where they belong."

The sanctions will be effective "immediately," Mnuchin said, and any purchases of Venezuelan oil by US entities would flow into blocked accounts -- money the US officials said would be released only to the legitimate leaders of Venezuela.

The oil sanctions represent the latest and most significant escalation of the Trump administration's pressure campaign aimed at ousting Maduro from power. President Donald Trump last week recognized Venezuelan opposition leader Juan Guaido as the legitimate interim president of Venezuela and the US has continued to ramp up pressure on Maduro to resign.

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