Italian prosecutors are investigating derivatives trades made by the country's largest banks, judicial sources said on Friday, as the scandal involving the troubled Monte dei Paschi appeared to spread to other lenders.

Dozens of people at Monte dei Paschi, UniCredit, Intesa Sanpaolo, BNL and Credem are being investigated by a court in Trani, Italy, for suspected usury and fraud related to derivatives contracts signed by the banks, the sources said. (Reporting by Vincenzo Damiani in Bari. Writing by Steve Scherer.)