HSBC USA has received grand jury subpoenas, as well as requests for further information, from the Department of Justice and the US Attorney's Office.
The case is said to be focused on its global banknotes and foreign correspondent unit, which distributes capital to central banks, large commercial financial institutions and currency exchanges, reports the Financial Times.
Last month, HSBC said it had decided to close the business following an internal strategic review.
A statement from the bank on the investigation said: "We take regulatory matters very seriously and are working closely with our regulators and actively resolving these issues."
It added that if it is found to have breached the law, a financial penalty may be imposed.
Earlier this month, it was reported by the Financial Times that HSBC is close to agreeing a deal to sell $4.3 billion worth of US car loans on to Santander.
By Tony Aynsley