Bitcoin's extreme volatility has flustered lawmakers and regulators.

"There are many problems" with the way bitcoin markets operate, testified Securities and Exchange Commission Chairman Jay Clayton at a Senate Banking Committee hearing on cryptocurrency oversight Tuesday.

Clayton and Chris Giancarlo, chairman of the Commodity Futures Trading Commission, testified that tighter regulation and a more coordinated response between federal agencies were needed to protect investors from fraud and abuse in digital currency markets.

Securities and commodities laws protecting investors don't neatly apply to new online currency trading. Regulators have trouble enforcing the laws, because it's not entirely clear what bitcoin is or does. Is bitcoin a currency? A security? Something entirely different?

"What's so challenging about bitcoin is that it has characteristics of multiple different things," Giancarlo said.

Although Clayton said it was too soon to know whether Congress needed to enact laws targeting cryptocurrencies, he said, "We may be back with our friends from Treasury and the Fed to ask for additional legislation."

Clayton said investors raising money through initial coin offerings are similar to investors buying stocks. That makes bitcoin like a security, and it falls under SEC enforcement.

Related: Bitcoin was $800 a year ago. Now it's $17,000

Bitcoin's price skyrocketed in 2017 to above $19,000 on mostly unregulated trading platforms.

"It's nothing short of remarkable," Ohio Sen. Sherrod Brown said of bitcoin's rise.

As interest soared, however, "fraudsters and other bad actors [preyed] on this enthusiasm," Clayton said. Two weeks ago, hackers stole $530 million from a Japanese currency exchange.

"We must crack down hard on those who try to abuse [investors'] enthusiasm with fraud and manipulation," Giancarlo said.

Bitcoin tumbled as much as 13% during the day to below $6,000 for the first time in three months.

It clawed back losses during morning trading and was back up above $7,00. Bitcoin has lost close to two-thirds of its value since it peaked above $19,000 in December.

Related: Bitcoin and other cryptocurrencies tank

Cryptocurrency investors have been alarmed by sharpened rhetoric around online currencies in recent weeks.

In Tuesday, Switzerland-based Bank for International Settlements General Manager Agustin Carstens called bitcoin a "combination of a bubble, a Ponzi scheme and an environmental disaster."

Carstens' comments followed scrutiny Monday from Mario Draghi, president of the European Central Bank. Draghi said online currencies were "very risky assets" and that prices were "entirely speculative."