US banking giant Citigroup Monday reported a 30 percent increase in first-quarter net income from a year earlier due to higher revenues and lower net credit losses. Citigroup posted net income of $3.8 billion on revenues of $20.5 billion in the first quarter of 2013, up from $2.9 billion on $19.4 billion in the year-ago quarter. A key driver of the earnings increase was lower net credit losses, the ratio of current credit-related losses on a mortgage-backed security to the original value of the security, the bank said in a statement. Citi reported a loss of $3 billion in this category compared with $4 billion in the year-ago period. "During the quarter, we benefited from seasonally strong results in our markets businesses, sustained momentum in investment banking, continued year-over-year growth in loans and deposits in Citicorp, and a more favorable credit environment," said Citigroup chief executive Michael Corbat. "However, the environment remains challenging and we are sure to be tested as we go through the year."