JPMorgan Chase & Co. Chief Executive Officer Jamie Dimonsaid traders in a London unit responsible for a $2 billion lossdidn't understand the risks they were taking and weren't properlymonitored.

“This portfolio morphed into something that, rather than protectthe firm, created new and potentially larger risks,” Dimon said inprepared remarks ahead of his appearance tomorrow before theSenate Banking Committee. “We have let a lot of people down, and weare sorry for it.”

Lawmakers plan to question Dimon at hearings this week and nextabout the bank's blunders on credit derivatives in its chiefinvestment office after he initially called April news reportsabout the trades “a complete tempest in a teapot.” Shares of thebank, the biggest in the U.S., have dropped 17 percent since Dimondisclosed the mounting losses May 10, lopping about $26.5 billionfrom the firm's market value.