FBI Director Robert Mueller says there has been a “tremendous surge” in mortgage fraud investigations, and he expects it to keep growing.

At a Senate hearing Wednesday, Mueller (MAHL’-ur) estimated that the FBI has 1,300 investigations underway, 19 of them involving sub-prime lending practices by U.S. financial institutions.

That’s up from three months ago, when FBI officials said they were investigating 14 companies for possible fraud or insider trading violations.

Mueller says the number of inquiries has increased to a level that required shifting agents from other projects onto mortgage fraud.