The Federal Deposit Insurance Corp. said Friday that the U.S. banking sector lost even more money last quarter than initially reported, due to "significant amendments" to writedowns on troubled assets.

The U.S. banking sector lost $32.1 billion last quarter, up from an initial report of $26.2 billion. Net income for the entire year dropped to $10.1 billion from an initial figure of $16.1 billion. The FDIC said that banks reported big changes shortly after the data were originally released on Feb. 26.

The results represent the banking sector's first loss in nearly two decades as bad loans and other assets "overwhelmed" revenue, the federal banking regulator said. Loan losses doubled from a year earlier and return on assets fell to -0.77%, the lowest level since 1987.

The number of federally insured banks contracted by 79 institutions last quarter, according to the revised Quarterly Banking Profile. The agency's list of "problem banks" at risk of failure rose to 252 banks, from 171 in the previous quarter, and 76 a year earlier.

The FDIC is currently stress-testing banks that have received capital from the government TARP program to ensure that they can survive a more severe economic downturn.

At-risk institutions hold $159 billion in assets, up from $116 billion at the end of the third quarter, and $22 billion at the end of 2007.

The FDIC said the industry lost $26.2 billion last quarter, a year after the recession officially began. It was the banking sector's first loss since the same period in 1990, as loan losses doubled from a year earlier and return on assets fell to -0.77%, the lowest level since 1987.

The FDIC said that while four institutions accounted for half the industry loss, "earnings problems were widespread." One out of three banks reported a loss during the fourth-quarter, according to the regulator, including large, high-profile firms like Bank of America ( BAC), Citigroup ( C) and Wells Fargo ( WFC).

While banks reported big losses, they also increased net interest income -- the amount of money gained from customer interest payments, less the amount banks spend to borrow funds. Net interest income rose $4.5 billion, or 4.9%, to $97 billion from a year earlier. However, the increase was weighted to large institutions, while community banks suffered the lowest interest margins in 20 years.