Italian police announced on Friday they had seized fake US Treasury bonds with a face value of $6 trillion in Switzerland, a media report said.
The bonds, more than a third of US national debt, were found inside makeshift compartments in three reinforced metal crates in Zurich, the prosecutors from the southern Italian city of Potenza said in a statement.
US officials confirmed the bonds, dated 1934, were counterfeit, the prosecutors said.
"These fictitious bonds were apparently part of a plan to defraud some Swiss banks," the US embassy in Rome said in a statement.
Italian prosecutors said criminals had attempted to sell the bonds to emerging markets or use them to get loans from banks.
Eight Italian members of a criminal network were arrested for international fraud and other financial crimes, the police said.