US senators Friday blasted banking giant JPMorgan Chase over its mammoth trading losses on complex derivatives last year and called for tougher regulatory scrutiny of the banking industry. Senator Carl Levin, at a hearing on JPMorgan's ill-fated "whale" trades, slammed the bank's trading operation that lost $6.2 billion over just a few months in 2012 as a "runaway train barrelling through every risk limit." "Derivative values that can't be trusted are a serious risk to our financial system," said Levin, the chairman of the Senate subcommittee on investigations. The incident is a "reminder you just can't rely on a major bank... without a strong regulator looking over," Levin added. A 300-page report by the subcommittee said that JPMorgan kept adding risky bets on top of earlier ones, hid losses, disregarded its own rules for risk limits, avoided oversight by its regulator and "misinformed" investors, regulators and the public. Former and current JPMorgan executives testifying at the Senate hearing painted a picture of confusion and disbelief over the scale of the losses, which blindsided the Wall Street powerhouse in the first quarter of last year. Ina Drew, JPMorgan's chief investment officer at the time with responsibility for the London trading operation which racked up the losses, admitted errors even as she pointed the finger at others. "I was, and I remain, deeply disappointed and saddened that such significant losses occurred in the business unit I oversaw," said Drew, who resigned last year to take responsibility for the debacle, according to her prepared testimony. But Drew also pointed a finger at London employees that she said misled her on the scale of the problem and "let me, and the company, down." "Since my departure, I have learned of the deceptive conduct by members of the London team," she said. The losses, which JPMorgan initially played down when they were first reported in the media, rocked the US financial world after the bank proudly sailed through the US financial crisis with far less damage than its competitors. Rooted in bad trades of the bank's own money on complex derivatives, the losses were first blamed on one trader who was nicknamed the London Whale for the size of his positions in financial markets. The whale scandal cast a pall over the largest US bank, which was hailed during the financial crisis for its comparatively strong risk management practices. Senators pressed for details on what happened, suggesting JPMorgan sought to conceal the risks it took from regulators. They also pushed to know more about the role of JPMorgan chief executive Jamie Dimon. In January, the bank board slashed in half the bonus of Dimon, who initially downplayed the scandal as a "tempest in a teapot." While Dimon was not testifying on Friday, Levin has said the committee may hold additional hearings. Senators questioned Peter Weiland, the former head of market risk in the chief investment office, who dismissed as "garbage" an early 2012 internal JPMorgan analysis that said the bank risked losses totalling $6.3 billion. Weiland acknowledged that his choice of words was "not appropriate." But he suggested he simply had not understood that such deep losses were possible. "My first reaction was 'doesn't look right,'" Weiland said. "Clearly it turned out to be predictive." Senators asked witnesses whether the fiasco again demonstrates the problem of financial institutions that are "too big to fail." Senator John McCain pressed JPMorgan's acting chief risk officer Ashley Bacon what he should tell constituents who were angered that the government used taxpayer money to bail out banks hit by their own risky behaviour. "Management oversight on the ground in London failed miserably," Bacon replied. Shares in JPMorgan were down nearly 2.0 percent in early-afternoon trading, also hit by a Federal Reserve review telling the bank it needs to quickly address "weaknesses" in its capital plan before it expands dividend payments and share buybacks that benefit shareholders.