US authorities are investigating Fiat Chrysler's reporting of US sales, the auto giant said Monday.

FCA pledged to "cooperate fully" with the probes by the Securities and Exchange Commission and the Justice Department which, according to Bloomberg, are examining whether the carmaker violated US securities laws.

In January a Fiat Chrysler auto dealers group accused FCA US of financially rewarding dealerships that falsely reported higher car sales, inflating the auto giant's results.

Dealers of the Napleton group in Illinois and Florida sued FCA US for racketeering and fraud and said the company's practices unfairly harmed their businesses, which declined the payments.

The lawsuit also challenged the validity of FCA sales figures that have shown rapid growth.

FCA strongly denied the allegations, dismissing the arguments as the product of "two disgruntled dealers" who failed to fulfill their commitments to FCA.