Federal Reserve chair Janet Yellen called bitcoin a "highly speculative asset" that isn't subject to regulation by the U.S. central bank during her final press conference today.

Yellen, whose term in office expires in February, spoke to reporters today on a range of topics. About thirty minutes into the presser, Yellen was asked about bitcoin.

She noted that, in the Fed's view, bitcoin "plays a very small role" in the U.S. payment system, going on to explain:

Yellen went on to answer a follow-up question on directives for banks regarding bitcoin. She answered by saying that, to date, the Fed has not issued any specific missives to banks on the subject.

Her comments didn't represent much of a departure from past statements – she told Congress in 2014 that the Fed wouldn't move to regulate bitcoin activity, while also calling blockchain an "important technology" earlier this year.

Indeed, compared to central banks like those in countries like China, the Fed has largely maintained a hands-off approach to the cryptocurrency, focusing primarily on research.

And perhaps disappointingly for some observers in the bitcoin community, there were no "buy bitcoin" signs on display during Yellen's appearance today.

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