The Federal Bureau of Investigation has opened criminal inquiries into 14 companies as part of a wide-ranging investigation of the troubled mortgage industry, F.B.I. officials said Tuesday.

The F.B.I. said it was looking into possible accounting fraud, insider trading or other violations in connection with loans made to borrowers with weak, or subprime, credit.

The agency declined to identify the companies under investigation but said the inquiry, which began last spring, involves companies across the financial industry, including mortgage lenders, loan brokers and Wall Street banks that packaged home loans into securities. It is unclear when charges, if any, might be filed.

As part of its investigation, the F.B.I. is cooperating with the Securities and Exchange Commission, which is conducting about three dozen civil investigations into how subprime loans were made and packaged, and how securities backed by them were valued. State prosecutors are also investigating various areas of the mortgage industry.