U.S. authorities are looking at some "relatively large corporations" as part of a sweeping mortgage fraud investigation, Federal Bureau of Investigation Director Robert Mueller said Thursday.

Nineteen companies, including mortgage lenders, investment banks, hedge funds, credit-rating agencies, and accounting firms, are being investigated, federal officials said at a press conference.

The Justice Department and FBI officials announced that roughly 400 people have been charged for roles in home-lending schemes; 60 were arrested Wednesday. FBI officials estimate that the losses from the alleged scams reached $1 billion.

Also Thursday, an indictment announced in New York accused two former Bear Stearns Cos. managers of misrepresenting to investors the condition of two hedge funds that lost $1.4 billion on mortgage-related assets. According to the nine-count indictment, Ralph R. Cioffi and Matthew M. Tannin have been charged with conspiracy, securities fraud, and wire fraud. Mr. Cioffi was also charged with insider trading.

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