WASHINGTON — A former top Citigroup Inc. underwriting executive warned company leaders of "extreme risks" and potential large losses in the company's subprime-mortgage approval process beginning in 2006, according to his testimony before a congressional panel.

The executive, Richard Bowen III, said he objected repeatedly to the company's approval of billions of dollars worth of mortgages that failed to meet various underwriting criteria. In November 2007, he sent an email to Citigroup executives including former Treasury Secretary Robert Rubin. In it, he warned of "breakdowns of internal controls and resulting significant but possibly unrecognized financial losses existing within our organization."

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