In the UK, the country's newly-established National Crime Agency warned that more arrests were on the way.
Most if not all the arrests took place within a couple of days of last week's capture of Silk Road's alleged mastermind, Ross Ulbricht, in San Francisco, suggesting that authorities may now be busy unraveling the network of drug dealers who made fortunes peddling illicit substances through the site.
"These latest arrests are just the start; there are many more to come," he said.
Silk Road gained widespread notoriety two years ago as a black market bazaar where visitors could buy and sell hard drugs using bitcoins, a form of online cash which operates independent of any centralized control.
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A so-called "hidden site," Silk Road used an online tool known as Tor to mask the location of its servers. While many other sites sell drugs more or less openly, Silk Road's technical sophistication, its user-friendly escrow system and its promise of near-total anonymity quickly made it among the best known.
"Any large sellers on Silk Road should be very nervous," said Nicholas Weaver, a researcher with the International Computer Science Institute in Berkeley and the University of California, San Diego.
Silk Road's eBay-style customer review system means that months' worth of sales history are now in law enforcement hands, Weaver said in an email, while the traceable nature of bitcoin transfers means the FBI "can now easily follow the money.