Several investment firms are being investigated over whether they made improper payments to intermediaries to gain business from New York state's pension fund, sources familiar with the investigation said on Tuesday.

The inquiry by New York state's top legal officer and the U.S. Securities and Exchange Commission includes Carlyle Group , one of the world's largest private equity firms, said the sources, who asked not to be identified because of the ongoing investigation.

The office of New York Attorney General Andrew Cuomo declined to comment. A spokesman for the SEC declined comment.

Carlyle spokesman Christopher Ullman said in an email that the firm has fully cooperated with Cuomo's office.

We understand this is an industry-wide investigation and that we are not the focus of the investigation.

Carlyle said it serves pensioners in the states of New York, Illinois and Connecticut.

Last month, Henry Morris, the former New York state comptroller's top fund-raiser, and David Loglisci, the state's pension investment chief, were charged with taking millions of dollars in kickbacks from money manager firms.

At the time, Cuomo and SEC chairman Mary Shapiro said the probes were continuing.

(Reporting by Grant McCool and Megan Davies in New York; Rachelle Younglai in Washington; Editing by Tim Dobbyn)