Citigroup Inc. provided more evidence Monday that America's big banks may have turned a corner. Citigroup said it earned $4.4 billion after payment of preferred dividends, compared with a loss of $696 million a year earlier. That was the bank's biggest quarterly profit since the second quarter of 2007. The company cited strong trading of bonds, stocks and other securities for its big profit. Citigroup, one of the hardest hit banks during the credit crisis and recession, said losses from bad loans fell for the third consecutive quarter. It also set aside less money for loan losses. Citigroup earned 15 cents per share on revenue of $25.4 billion. Yet CEO Vikram Pandit sought to dampen short-term expectations for Citigroup, saying the bank remained cautious “given the uncertain economic recovery and high unemployment in the US.” “Realistically, we do not expect our performance to follow an invariable trendline upward,” he said.