Fake US bonds worth $US6 trillion have been found in a warehouse in Zurich, Switzerland.
Italian agencies have arrested eight people and are investigating them for fraud.
Prosecutors say the fraud posed "severe threats" to international financial security.
In cooperation with Swiss police, they tracked down three metal boxes to a warehouse in Zurich.
The BBC reports the crates contained thousands of fake US bonds that gave appeared to have been issued by the US Federal Reserve in 1934.
US officials confirm that the bonds were counterfeit.
Italian authorities say the investigation that led to the discovery of started as an investigation into mafia loan sharking.
Police say the initial loan sharking investigation expanded as prosecutors used telephone and computer intercepts to unearth evidence of illegal activity surrounding Treasury bonds.
The BBC reports that fake US securities have been seized in Italy before. There were at least three cases in 2009.