Washington, July 20 (Reuters): The US justice department said today 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 US, 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 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.

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 totalling hundreds of thousands of dollars.

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.