The FBI is investigating four major U.S. financial institutions whose collapse helped trigger a $700 billion bailout plan by the Bush administration.

Two law enforcement officials said the FBI is looking at potential fraud by mortgage finance giants Fannie Mae and Freddie Mac, Lehman Brothers Holdings Inc., and insurer American International Group Inc.

A senior law enforcement official says the inquiries, still in preliminary stages, will focus on the financial institutions and the individuals that ran them.

Officials say the new inquiries brings the number of corporate lenders under investigation over the last year to 26.