FBI Director Robert Mueller on Wednesday confirmed that the agency has opened a "preliminary investigation" into JPMorgan Chase & Co (JPM), the nation's largest bank.

JPMorgan disclosed last week that it had suffered a multibillion-dollar trading loss due to a failed hedging strategy.

A person familiar with the matter said on Tuesday that the FBI's New York office has opened a preliminary probe into the loss, which has been estimated at more than $2 billion.

Mueller was testifying before the Senate Judiciary Committee.

When pressed by lawmakers about what legal violations JPMorgan may have committed, Mueller said: "All I can say is we've opened a preliminary investigation."

Mueller also said the timing of the investigation "depends on a number of factors." He did not elaborate.