JPMorgan Chase, which emerged from the financial crisis as the nation’s biggest bank, disclosed Thursday that it lost more than $2 billion in trading, a surprising stumble that promises to escalate the debate over whether regulations need to rein in trading by banks.

Jamie Dimon, the chief executive of JPMorgan, blamed “errors, sloppiness and bad judgment” for the loss, which stemmed from a hedging strategy that backfired.

The loss, which could go higher, is a rare blow to the reputation of Dimon, 56. After successfully steering his bank through the market turmoil of 2008 and the recession, he is perhaps the most influential bank executive in the country — and a vocal critic of the efforts to write rules under the Dodd-Frank regulatory overhaul.

The setback for JPMorgan may strengthen the hand of regulators in Washington who are now writing the rules for Dodd-Frank — in particular the Volcker Rule, which restricts banks from trading with their own money.

JPMorgan’s setback “casts doubt on Jamie’s opposition and adds fuel to anyone who has been pushing for greater regulation,” said Mike Mayo, an analyst with Credit Agricole Securities. “Oh, how the mighty have fallen.”

Questions over whether banks have been engaging in such trading for themselves while calling it “market making” or “hedging” came into focus last month, when reports emerged that a trading unit of JPMorgan in London was taking such large positions in the name of hedging that they were distorting the market.

At the time, Dimon played down concerns about that trading in what the bank calls its Chief Investment Office, telling analysts on an April 13 conference call that it was “a complete tempest in a teapot.”

In a hastily organized conference call with analysts Thursday, Dimon sounded more humble, saying that “egregious mistakes” were made.

Yet while conceding that the bank had “egg on its face,” Dimon refused to concede that the losses necessitated a stronger regulatory framework.

The troubles are expected to weigh on the bank’s broader earnings. For example, the corporate group, which includes the Chief Investment Office, is now expected to lose $800 million in the second quarter, the company said in the filing. Previously, JPMorgan had estimated that the group would report net income of roughly $200 million.

Shares of JPMorgan tumbled 6.7 percent in after-hours trading. Its Wall Street rivals were also down sharply.