Washington: The US Justice Department said on Thursday it had shut down the dark web marketplace AlphaBay, working with international partners to knock offline the site accused of allowing a global trade in drugs, firearms, computer hacking tools and other illicit goods.

Authorities said the law enforcement action was one of the largest ever taken against criminals on the dark web, part of the internet that is accessible only through certain software and typically used anonymously.

AlphaBay allowed users to sell and buy opioids, including fentanyl and heroin, contributing to a rising drug epidemic in the United States, Attorney General Jeff Sessions said at a news briefing in Washington, DC to announce the action.

"The dark net is not a place to hide," Sessions said. "This is likely one of the most important criminal investigations of the year - taking down the largest dark net marketplace in history.

The Justice Department said law enforcement partners in the Netherlands had taken down Hansa Market, another dark web marketplace.

AlphaBay and Hansa Market were two of the top three criminal marketplaces on the dark web, Europol chief Rob Wainwright said at the press conference.

The move struck a blow to an international drug trade that has increasingly moved online in recent years, though some experts thought its impact would be limited.

"The takedown of AlphaBay is significant, but it's a bit of a whac-a-mole," said Frank Cilluffo, director of the Centre for Cyber and Homeland Security at George Washington University.

Criminals, he said, "are going to flock to other places."

AlphaBay mysteriously went offline earlier this month, prompting speculation among its users that authorities had seized the site. It was widely considered the biggest online black market for drugs, estimated to host daily transactions totaling hundreds of thousands of dollars.

The international exercise to seize AlphaBay's servers also involved authorities in Thailand, Lithuania, Canada, Britain and France.

The operation included the arrest on July 5 of suspected AlphaBay founder Alexandre Cazes, a Canadian citizen arrested on behalf of the United States in Thailand.

Cazes was logged on to AlphaBay at the time of his arrest, allowing authorities to find his passwords and other information about the site's servers, according to legal documents.

Cazes, 25, apparently took his life a week later while in Thai custody, the Justice Department said. He faced charges relating to narcotics distribution, identity theft, money laundering and related crimes.

FBI Acting Director Andrew McCabe said AlphaBay was ten times as large as Silk Road, a similar dark website the agency shut down in 2013.

About a year later, AlphaBay was launched, growing quickly in size and allowing users to browse goods via the anonymity service Tor and to purchase them with bitcoin currency.

Reuters