Shares of JPMorgan Chase & Co. tumbled in premarket trading as a published report said that the bank's trading losses may be as much as $9 billion - far higher than the estimated $2 billion loss disclosed last month.
In May, JPMorgan said the loss came from trading in credit derivatives that was designed to hedge against financial risk, and not to make a profit for the bank.
The New York Times, citing sources it did not identify by name, said that the losses have grown recently as JPMorgan has been unwinding its positions. It said its sources were current and former traders and executives at the bank.
The bank plans to give more details related to its losses when it reports second-quarter earnings on July 13.
JPMorgan's stock dropped $1.79, or 4.9 percent, to $34.99 in premarket trading.
A company representative could not be immediately reached for comment.