* Investigators checking if execs failed to report allegations -newspaper

* Also checking whether Dunn used company-leased aircraft -paper

* Best Buy declines comment

May 10 (Reuters) - Best Buy Co Inc has expanded the probe into the personal conduct of its former chief executive, and is now investigating whether senior officials at the world's largest consumer electronics chain failed to report allegations about the ex-CEO to its board, the Minneapolis Star Tribune reported on Thursday.

A spokesman for the company declined comment.

The report came a month after CEO Brian Dunn resigned abruptly from Best Buy during a company probe into allegations of personal misconduct.

The Minneapolis Star Tribune and other media have reported that Best Buy's audit committee was investigating whether Dunn used company resources to carry on an inappropriate relationship with a female staffer.

The company's investigators already have spoken to the 29-year-old woman, and she has retained a lawyer, the newspaper reported, citing a source close to the Richfield, Minnesota-based retailer.

Investigators are also looking into whether Dunn used company-leased aircraft in connection with the alleged relationship, the newspaper reported, citing a person with knowledge of the investigation.

Best Buy leased and chartered aircraft services from Best Jets International, which is owned by company founder and chairman Richard Schulze, for about $3.6 million over the past five years, documents filed with the U.S. Securities and Exchange Commission showed.

The terms of Dunn's resignation, including whether he will obtain any severance pay from his employer of almost three decades, have not been announced.

Dunn's compensation for the fiscal year ended March 3 has not been approved by the company's compensation committee, pending the results of the probe, a regulatory filing on Wednesday showed.

"The results of that investigation will be made publicly available and the final terms of Mr. Dunn's separation will be disclosed ... when completed," the company said.

Dunn, who started at Best Buy as a sales associate and rose through the ranks to become CEO in June 2009, would not be entitled to any severance payment if he resigned voluntarily, according to the proxy filing.

Best Buy shares slipped 0.8 percent to close at $19.94 on Thursday.