US prosecutors said a suitcase filled with nearly US$800,000 was brought into Argentina from Venezuela as a campaign contribution allegedly intended for Argentina's newly elected president.
The charges drew a strong rebuke from Venezuelan President Hugo Chavez's government, which called it a "fabricated scandal."
The disclosure came on Wednesday in a Miami court hearing for a criminal complaint against four men arrested and charged with being Venezuelan agents who attempted a cover-up.
US prosecutors said recorded conversations of those involved indicate the scheme reached to the highest levels of the Venezuelan government.
But Venezuelan Foreign Minister Nicolas Maduro called the charges "a desperate effort by the United States government using ... the judicial branch for a political, psychological, media war against the progressive governments of the continent."
The allegations of campaign funding sent clandestinely from Caracas to Buenos Aires will give new ammunition to Chavez's critics who accuse him of meddling in other Latin American countries and using oil money to bolster alliances.
The complaint said "neither the true source nor the intended recipient of those cash funds had been disclosed." Assistant US Attorney Thomas Mulvihill said in court, however, that the FBI recorded a conversation in which one of those arrested said the Fernandez campaign was the intended recipient of the money, which was seized by Argentine customs authorities in August.
Charged with failing to register with the US as agents of a foreign power were Venezuelans Moises Roman Majonica, 36; Franklin Duran, 40; and Carlos Kauffmann, 35; and Uruguayan Rodolfo Wanseele, 40. All will remain in custody pending a bail hearing on Monday.
If convicted, they face up to 10 years in federal prison.
The Venezuelan-American man who carried the suitcase, Guido Alejandro Antonini Wilson, is not charged in the case. Argentina asked the US in August to extradite him on fraud charges, but the new case suggests he has gone from suspect to key witness.
As soon as the cash was seized, "we saw it as a political-media ambush," Maduro told state television. He blamed a US "campaign that since August has sought to sully our government's relations with South America."
Kenneth Wainstein, Assistant US Attorney General for National Security, said the complaint "outlines an alleged plot by agents of the Venezuelan government to manipulate an American citizen in Miami in an effort to keep the lid on a burgeoning international scandal."
Prosecutors said in court that evidence against the men includes FBI recordings of conversations between some of them and senior officials in Venezuela's office of the vice president, intelligence service and justice ministry.
RSS