Four men have been arrested over their alleged roles in illegal drug marketplace Silk Road.
Three men aged in their early 20s were detained in Manchester while a fourth, in his 50s, was arrested in Devon.
They were initially arrested on suspicion of drug offences, and more arrests are expected in the coming weeks after the alleged operator of the website, Ross Ulbricht, was arrested in San Francisco by the FBI at the start of the month.
Last week 40-year-old Steven Lloyd Sadler, allegedly one of the biggest sellers on the site, was arrested in Seattle.
Silk Road operated on Tor, the 'hidden internet' which anonymises user activity by operating under layers of encryption.
Keith Bristow, the National Crime Agency's director general, said: "These arrests send a clear message to criminals; the hidden internet isn't hidden and your anonymous activity isn't anonymous. We know where you are, what you are doing and we will catch you."
The site dealt in various illegal goods but was notable for its trade in drugs, paid for with the virtual currency Bitcoin.
The value of the currency plunged 20% after online drug marketplace Silk Road was shut down by the FBI.
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