Some observers pinned the latest retreat on an exchange hack in South Korea, while others pointed to lingering concern over a clampdown on trading platforms in China. Cryptocurrency venues have come under growing scrutiny around the world in recent months amid a range of issues including thefts, market manipulation and money laundering.

Bitcoin has dropped about 12 percent since 5 p.m. New York time on Friday and was trading at $6,756, bringing its decline this year to 53 percent. Most other major virtual currencies also retreated, sending the market value of digital assets tracked by Coinmarketcap.com to a nearly two-month low of $298 billion. At the height of the global crypto-mania in early January, they were worth about $830 billion.