The regulator for mortgage companies Fannie Mae and Freddie Mac has sued Swiss bank UBS to recover more than $900 million (SFr723 million) of losses.
It is alleged that UBS misled the housing agencies into buying $4.5 billion of risky mortgages.
The United States Federal Housing Finance Agency (FHFA) said it also planned more lawsuits to recover additional losses by Fannie Mae and Freddie Mac from investments in private-label debt.
In July 2010 the FHFA issued 64 subpoenas to banks, seeking details about subprime and other mortgage debt that Fannie Mae and Freddie Mac bought when the housing market was healthy.
The UBS case is seen as part of a push by Washington to hold banks responsible for the nation's housing problems. It is also the latest effort to prop up the government-sponsored enterprises (GSEs), whose September 2008 federal seizure has so far cost taxpayers more than $135 billion.
"From the issuance of 64 subpoenas last year to the filing of this lawsuit and further actions to come, we continue to seek redress for the losses suffered," FHFA Acting Director Edward DeMarco said in a statement on Wednesday.
The GSEs remain crucial to the housing market, having in 2010 guaranteed 70 per cent of single-family mortgage-backed securities that were issued and having provided $1.03 trillion of market liquidity, a FHFA report to Congress last month showed.
UBS has made no immediate comment.
swissinfo.ch and agencies