US mortgage giant Fannie Mae has sued nine banks including UBS and Credit Suisse for the alleged manipulation of key interbank lending rate Libor.

The US mortgage financier in its lawsuit filed to the US District Court in Manhattan has alleged that it lost money on a range of financial products as a result of manipulation of Libor.

Fannie Mae is seeking more than US$800 million in damages.

The other seven banks being sued are Barclays, RBS, Deutsche Bank, Bank of America, Citibank, JPMorgan, and Rabobank.

Many of those have already admitted wrongdoing and settled with regulators. Barclays, UBS and RBS have paid fines totalling US$2.5 billion in regards to the charges, Rabobank and European financial firm ICAP have also paid Libor-related fines; overall, these five banks have paid US$3.7 billion in settlements with US and UK regulators.

In March this year, mortgage financier Freddie Mac also sued more than a dozen banks over similar allegations.

Freddie Mac and Fannie Mae use Libor to determine interest payments on their investments in floating-rate financial instruments such as bonds and swaps.