The banks include UBS Group AG (>> UBS Group AG), BNP Paribas SA (>> BNP Paribas) and Royal Bank of Scotland Plc (>> Royal Bank of Scotland Group plc), Bloomberg reported, citing people familiar with the matter.
A series of class action lawsuits have accused various banks and brokerages of conspiring to manipulate U.S. Treasury auctions.
The lawsuits have alleged that the banks colluded to manipulate Treasury Department auctions and the pricing of Treasury securities, as well as derivative products such as futures, whose value is pegged to the Treasury.
UBS has flagged a probe related to U.S. Treasury securities in its earnings reports.
"UBS and reportedly other banks are responding to investigations and requests for information from various authorities regarding U.S. Treasury securities and other government bond trading practices," the Swiss bank said in its latest quarterly report last month.
UBS, BNP Paribas and the U.S. Justice Department all declined to comment when contacted by Reuters. RBS did not immediately respond to a request for comment.
(Reporting by Subrat Patnaik in Bengaluru and Karen Freifeld in New York; Editing by Sai Sachin Ravikumar)