Billionaire investor Warren Buffett offered no comment Monday as he showed up to meet with regulators who are looking into transactions between insurer American International Group Inc. and a unit of Buffett’s company, Berkshire Hathaway Inc.

Buffett, accompanied by one man believed to be a Berkshire Hathaway attorney, entered a side door at the Woolworth Building in lower Manhattan where the Securities and Exchange Commission has a regional office.