Treasury Secretary Jack Lew called bitcoin a "phenomenon," but told CNBC on Thursday that the U.S. government needs to make sure the digital currency doesn't become a funding haven for criminals and terrorists.
In an interview at the World Economic Forum in Davos, Switzerland, Lew told "Squawk Box" he has spoken to JPMorgan Chairman and CEO Jamie Dimon about bitcoin, and the two share a certain "incredulity" about it.
(Read more: Dimon: Economy starting to fire on all cylinders)
"From the government's perspective, we have to make sure [bitcoin] does not become avenue to funding illegal activities or to funding activities that have malign purposes like terrorist activities," Lew said.
"It is an anonymous form of transaction. And it offers places for people to hide."
(Read more: Treasury launches new security—first in 17 years)