FILE PHOTO: Logos of Swiss bank UBS are seen at a branch office in Zurich, Switzerland January 27, 2017. REUTERS/Arnd Wiegmann

(Reuters) - U.S. federal prosecutors subpoenaed several banks last month as part of a criminal investigation into possible manipulation of the U.S. Treasuries market, Bloomberg reported on Monday.

The banks include UBS Group AG UBSG.S, BNP Paribas SA BNPP.PA and Royal Bank of Scotland Plc RBS.L, 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.