The U.S. investigation into alleged manipulation of interbank lending rates is focusing on possible violations of a commodities law that has previously been used to send financial executives to prison, the Financial Times reported on Thursday.

The newspaper cited people familiar with the probe into the setting of London and Tokyo interbank offered rates as saying U.S. authorities are modeling their investigation on a past prosecution of three energy companies for violations of the Commodity Exchange Act, which resulted in criminal settlements and prison terms of up to 14 years.

The interbank lending probe, led by the U.S. Commodity Futures Trading Commission (CFTC) and the Department of Justice, is examining possible collusion between traders and bank treasury departments in 2007 and 2008.

In the investigation, authorities are examining whether Libor, and Tibor, the smaller Tokyo-based version, were rigged at the height of the financial crisis.

The CFTC is examining whether traders placed bets on future yen and dollar rates and colluded with bank treasury departments, who help set the Libor index, to move the rates in their direction, the FT said citing people familiar with the probe.

The CFTC was not immediately available for comment, but it has a policy of not commenting on open investigations.

(Reporting by Stephen Mangan; editing by Carol Bishopric)