NEW YORK — JPMorgan Chase, the largest bank in the United States, said this morning that a trading blunder had cost the bank $4.4 billion since the beginning of April, more than double its original estimate.

The bank said all managers in the London office responsible for the trade had been dismissed without severance pay and that it planned to revoke two years’ worth of pay from each of those executives.

JPMorgan’s original estimate of the trading loss, disclosed in May, was $2 billion.

The bank said that it was reducing its net income for the first quarter by $459 million because it had discovered information that “raises questions about the integrity” of values placed on certain trades.

“We don’t take it lightly,” CEO Jamie Dimon told Wall Street analysts on a conference call. He added: “We’re not making light of this error, but we do think it’s an isolated event.”

Dimon said the bank had closed the division of the bank responsible for the bad trade and moved the remainder of the trading position under its investment banking division.

Overall, JPMorgan said it earned $5 billion, or $1.21 per share, for the second quarter, which covers April through June and includes the bank’s disclosure of the trading loss on May 10.