WASHINGTON—The top U.S. anti-money-laundering regulator on Monday told a Bitcoin trade group that exchanges for the virtual currency must follow the same rules as established financial institutions, highlighting the government's efforts to keep tabs on a small but growing segment of the financial world.

The Treasury Department's Financial Crimes Enforcement Network, or Fincen, hosted the Bitcoin Foundation and other regulators and law-enforcement officials as the sides grapple with the rise of virtual currencies. Such digital...