The biggest coin climbed almost 55 percent in nine days after Facebook unveiled its plans for Libra on June 18, touching an 18-month high of almost US$14,000. According to him, crypto is not money, it's based on thin air, and is highly volatile with unregulated coins facilitating illegal activities, such as drug trade.
He also warned Facebook and other companies that, should they launch their own cryptocurrency, they would have to abide by both American and worldwide banking regulations.
JPMorgan Chase & Co, the largest U.S. bank by assets, also plans to launch its own digital coins.
After criticizing cryptos, Trump praised the US dollar as the most "dominant" currency in the world. The world is unsure of how successful or disruptive Libra will be, and on Thursday the cryptocurrency got perhaps its biggest detractor yet: the president of the United States.
The ubiquity of smartphones means digital wallets for Libra could expand the use of banking, credit card services and e-commerce in developing nations.
Powell said the Fed had established a working group to follow the project and was coordinating with other countries' central banks, several of which have also expressed concern about Facebook's project.
Powell stressed that before proceeding, Facebook needs to address "serious concerns" in regards to "privacy, money laundering, consumer protection and financial stability".
"I think we need to do a very careful, patient, thorough assessment of what the risks really are", Jerome Powell said Thursday, adding that the size of Facebook's social media network points to Libra's "systemic importance".