Fannie Mae sued nine banks, alleging that their manipulation of the benchmark London interbank offered rate (Libor), which four of them have admitted, cost the mortgage-financing company about $800 million.

The U.S. government-owned firm alleged that the banks, including Bank of America Corp., JPMorgan Chase & Co., and Citigroup Inc., acted to suppress the rate through quotes they submitted to the British Bankers Association, according to the complaint filed yesterday in Manhattan federal court.

Global authorities have been investigating claims that more than a dozen banks altered submissions used to set benchmarks such as Libor to profit from bets on interest-rate derivatives or to make the lenders' finances appear healthier.