The US Treasury placed four serving or retired Venezuelan generals on its sanctions blacklist Friday, raising pressure on the embattled government of President Nicolas Maduro.

The Treasury Department alleged that the four were either involved in repressing protesters or tied up in major corruption schemes.

Washington has already targeted Maduro himself for sanctions, and is a long-standing opponent of what it sees as his increasingly authoritarian regime.

Falling oil prices, political unrest, and corruption have decimated the country's economy and led to deadly protests under Maduro.

The new sanctions "highlight that corruption and repression continue to flourish under the Maduro regime, both by those in current government positions and former officials who continue to benefit from a corrupt system," the Treasury said.

Venezuelan Foreign Minister Jorge Arreaza said in a Twitter post following the US announcement that Caracas' military would never kowtow to Washington.

The army "will never bow to any foreign power, much less to the imperialist and warlike forces of Donald Trump's supremacist government. We demand respect," Arreaza wrote.

Delcy Rodriguez, president of Maduro's Constituent Assembly which effectively runs the country, said Trump "and his eccentric government should understand that Venezuela will never give in to blackmail or threats."

Treasury Secretary Steven Mnuchin said in a statement that "President Maduro and his inner circle continue to put their own interests above those of the Venezuelan people."

"This action underscores the United States' resolve to hold Maduro and others engaged in corruption in Venezuela accountable," he added.

"We call on concerned parties and international partners around the world to join us as we stand with the Venezuelan people to further isolate this oppressive regime."

Under the US Treasury order, Aragua state governor, retired general and state oil firm board member Rodolfo Clemente Marco Torres is designated for his alleged role in food smuggling.

Francisco Jose Rangel Gomez, another retired general and a former governor of Bolivar state, is accused of pressuring Venezuelan courts to release suspected members of armed pro-government gangs.

General Fabio Enrique Zavarse Pabon, commander of the defense zone that includes Caracas, is accused of using National Guard troops to violently repress demonstrations.

And Major General Jose Izquierdo Torres is accused of using his rank and position to corruptly enrich himself.

The Treasury order freezes any assets the four might have in US jurisdictions, and bans Americans and US firms from doing business with them.

US State Department spokeswoman Heather Nauert said the sanctions would only be removed if one day the officials change their behavior and respect the rule of law.

"Members of the Venezuelan armed forces who put their own interests above those of their fellow citizens cannot expect immunity from our sanctions and international accountability," she added.