The London trading debacle that JP Morgan boss Jamie Dimon once dismissed as a "tempest in a teapot" has so far cost the bank $5.8bn (£3.7bn), almost three times initial estimates, the bank said on Friday.

The bank made the admission as it released second quarter results that included a $4.4bn loss on the massive European trades known as "the London whale".

Dimon said the bank had clawed back two years of annual compensation from those involved in the trades. The bank also confirmed that the three traders at the heart of controversial trading had left.

The losses at JP Morgan's London offices have caused a political firestorm in the US and led to calls for tighter regulation of Wall Street banks. They come as the bank is also under investigation for its role in the alleged fixing of Libor interest rates.

JP Morgan held a two hour briefing with analysts on Friday morning to allay fears about the losses.

Finance chief Doug Braunstein put the trading loss at $5.8bn and confirmed that the bank believed it could lose between $800m and $1.7bn more as it tried to unwind the complex bets.

"We have put most of this problem behind us and we can now focus our full energy on what we do best – serving our clients and communities around the world," Dimon said in a statement.

JP Morgan reported net income of $4.96bn, or $1.21 a share, compared with $5.43bn, or $1.27 a share, a year earlier.

It also cut its previously reported first-quarter earnings by $459m, or 8.5%, after reviewing information that "raises questions about the integrity" of the CIO's credit portfolio. Dimon said there more losses to come of between $800m and $1.6bn.

At the analysts meeting, Dimon called the problem "isolated".

"At some point, I'd like people to actually focus on the underlying businesses … that's why we are here," he said.

Dimon initially dismissed reports about losses at the London operation as a "tempest in a teapot". But on Friday he conceded the trading mess had "shaken our company to the core".

The bank said Friday that it recently discovered information that suggests some individuals at the company may have tried to hide the full amount of the losses.

Mike Cavanagh, who headed the investigation of the London office, told analysts that the level of scrutiny at the London office "did not evolve commensurate with increasing complexity".

He said that Ina Drew, JP Morgan's chief investment officer, who oversaw the division responsible for the loss, had relied on traders assurances about their investments. "CIO failed to meet reasonable expectations," he said.

Drew left the bank days after the disclosure of the losses. In 2011, her pay package totaled $15m. Dimon said that her compensation, and those of three other executives, had been "clawed back".

The bank refused to give details on how much money had been forfeited by Drew or her former colleagues.

Dimon also moved to dismiss suggestions that the Libor investigation could prove as damaging to JP Morgan as it has to Barclays. Barclays has received a record fine and has axed its top three executives in the wake of the scandal.

"All I can say, like with all of these things, we are totally open with regulators," said Dimon. "I'd be a little patient if I were you. Not every company is in the same position."

Investors shrugged off the news. JP Morgan's shares rose more than 4% in early trading to $35.53. Analysts were encouraged by Dimon's comments on the US economy. JP Morgan's loans to small businesses were up 35% year on year.

"The fact is the economy isn't that bad for corporate America," said Dimon.

In an interview with Bloomberg, Warren Buffett, investment guru and chief of the Berkshire Hathaway investment company, said: "In terms of the loss from a transaction of that size, my guess is they pretty well worked out of it by now. It is a whole lot of money but it's not that significant, relative to JP Morgan."