Shares in America's biggest bank JP Morgan Chase have plunged after it revealed a surprise loss of $US2 billion due to mistakes made by its own traders.
The trades in credit derivatives were meant to protect the bank against risk.
After accounting for other gains, the final losses at its chief investment office (CIO) are estimated at $US800 million in the second quarter.
Chief executive Jamie Dimon said the loss could be as big as $US1 billion.
JPMorgan shares fell 6% after-hours, with other bank stocks following.
The CIO is an arm of the bank used to make broad bets to hedge its portfolios of individual holdings, the BBC reports.
Goldman Sachs, Citigroup and Bank of America also suffered heavy losses in electronic trading after the market close.
