"On July 14, 2011, Credit Suisse received a letter notifying it that it is a target of the Department of Justice investigation," said the bank in a statement.
"It has been reported that the US authorities are conducting a broader industry inquiry," it said, adding that the probe "concerns historical private banking services provided on a cross-border basis to US persons."
"Subject to our Swiss legal obligations, we will continue to cooperate with the US authorities in an effort to resolve these matters," said the bank.
The United States indicted four Credit Suisse bankers in February on charges of helping US taxpayers hide money in secret Swiss accounts to avoid US taxes.
At the time of that indictment, the bank said it was itself not part of the investigation.
The four bankers and unnamed co-conspirators were accused of offering US customers the chance to open accounts in Switzerland with the understanding that the money would be hidden from US tax authorities.
As of 2008, the bank hosted thousands of such accounts holding up to $3 billion in assets, the United States claimed.
The US probe against Credit Suisse comes after another damaging case against rival Swiss bank UBS.
Not only was UBS made to pay a $780 million fine, but the Swiss government was also forced to ease the country's banking secrecy rules to allow the bank to hand over 4,000 case files on US clients suspected of tax evasion.