Seventeen people have been arrested so far in an international crackdown on underground websites selling illegal drugs, a senior Europol official said.
Dutch prosecutors said the arrests came in the US, Ireland and Germany.
Troels Oerting, head of the police agency's cybercrimes division, said it co-ordinated raids in more than a dozen countries, including a US operation in which the FBI announced the arrest in San Francisco of a man accused of running the Silk Road 2.0 online drug bazaar.
"We will go after drug dealers regardless of whether they operate in the physical or virtual world," he said.
Europol said in addition to the Silk Road site, it had seized or shut down numerous other marketplaces with names such as Hydra, Cloud Nine, Pandora and Blue Sky, netting a million dollars (£630,000) in digital currency and 225,000 dollars (£142,000) of cash and drugs.
Silk Road and similar "darknet" websites are not visible on the open internet. They can only be accessed with special browsers that encrypt web traffic and transmit it via the Tor network of anonymising servers. Buyers and sellers trade using digital currencies, usually Bitcoin.
"I think there will be more than 55 different markets shut down," Mr Oerting said. "We didn't get (sites) Agora or Evolution, because there's only so much we can do on one day."
The FBI said it had arrested 26-year-old Blake Benthall on suspicion of running the Silk Road 2 site.
Mr Oerting declined to give more information on arrests in other countries because he said investigations were continuing.
"In the next wave we're going to come after people using these sites," he said.
Two men in Dublin were arrested yesterday as part of the crackdown on the darknet operations.
Six Britons have been also arrested on suspicion of being involved in running Silk Road 2.0 and one other illegal website.
They were a 20-year-old man from Liverpool, a 19-year-old man from New Waltham, Lincolnshire, a 30-year-old man from Cleethorpes, a 29-year-old man from Aberdovey, Wales, a 58-year-old man from Aberdovey, and a 58-year-old woman from Aberdovey.