Bitcoin tumbled 10 percent on Sunday to its lowest in two months, after a relatively small South Korean exchange said it was hacked.
Other major cryptocurrencies also fell. Ethereum dropped 14 percent to near $514 and litecoin fell more than 11 percent to around $104, according to CoinDesk.
The declines followed a report on Friday from The Wall Street Journal, citing sources, that U.S. regulators are investigating potential price manipulation at four major cryptocurrency exchanges: Bitstamp, Coinbase, itBit and Kraken.
The exchanges, CME and the Commodity Futures Trading Commission did not immediately respond to a CNBC request for comment on Sunday evening.