She said she regarded an initial indictment made public last month - charging Assange with a single count of conspiring with former Army intelligence analyst Chelsea Manning to hack a Defence Department computer password - as an attempt to "thread the needle and allege an underlying offence that did not seem like a political offence". It was a step debated but ultimately not taken by the Obama administration.
"For the first time in the history of our country, the government has brought criminal charges against a publisher for the publication of truthful information", said Ben Wizner of the American Civil Liberties Union.
But Justice Department officials sought to make clear that they did not view Assange's actions as protected by the First Amendment.
Ahead of department's national security division Assistant Attorney General John Demers called Mr. Assange as "No journalist".
The US Justice Department has now charged Assange with violating the US Espionage Act in the publishing of military and diplomatic files in 2010, rejecting his claim that he is a journalist. Among them is an espionage charge for publishing classified information - the first such indictment ever handed down against a non-government employee by the U.S. Justice Department.
On Friday the former Australian foreign minister Bob Carr said the severity of the potential sentence faced by Assange made the extradition request nearly as significant as if he were facing the death penalty.
"It's very, very unsafe", said Theodore J. Boutrous Jr., a media lawyer who represented CNN's Jim Acosta when he was barred from the White House for two weeks last November, among other high-profile cases.
WikiLeaks put itself on the map as a potent force in 2010 when it began publishing the files extracted from classified U.S. databases by Manning, then a low-level USA army intelligence analyst angered by the United States wars in Iraq and Afghanistan. It will fall on federal prosecutors to prove, for example, that he had "specific intent" to harm the United States and that his goal was not merely to shine a light on the USA military's conduct in the Middle East.
WikiLeaks used information from Manning to publish tens of thousands of U.S. government documents, including the names of people who helped American forces in Iraq and Afghanistan and United States diplomats around the world.
A selection of private medical files published by transparency website WikiLeaks as part of their global crusade to expose government secrets.
Chelsea Manning, the former Army intelligence officer who provided the documents released by WikiLeaks, condemned the indictments, declaring that administration officials "use the law as a sword, and have shown their willingness to bring the full power of the state against the very institution meant to shield us from such excesses". WikiLeaks did hide some names but then published 250,000 cables a year later without hiding the identities of people named in the papers.
"The indictment alleges that Assange published in bulk, hundreds of thousands of stolen classified documents". The allegations in Thursday's indictment are entirely separate from that episode.
The new charges relate to WikiLeaks' publishing of material obtained by Chelsea Manning, who gave the Assange reams of internal military and State Department documents.