WASHINGTON – Federal prosecutors charged WikiLeaks founder Julian Assange with espionage Thursday for conspiring to reveal national security secrets in what they described as one of the largest compromises of classified information in U.S. history.

The Justice Department revealed 18 charges against Assange. They include allegations that he aided and abetted former Army intelligence analyst Chelsea Manning's efforts to leak classified documents to the anti-secrecy group and committed a crime by publishing them on the internet.

“This release made our adversaries stronger and more knowledgeable, and the United States less secure," said John Demers, assistant attorney general for national security.

The charges are an escalation of the government's efforts to combat leaks of its secrets, and raised the difficult question of how – or whether – to distinguish WikiLeaks from journalists who frequently publish information the government would rather keep secret. They drew quick condemnation from advocates for press freedom.

Bruce Brown, the executive director of the Reporters Committee for Freedom of the Press, said criminalizing the receipt and publication of classified documents threatens all journalists. "Any government use of the Espionage Act to criminalize the receipt and publication of classified information poses a dire threat to journalists seeking to publish such information in the public interest," he said.

Assange has argued that he should be immune from prosecution as a journalist, authorities said he was charged for releasing a narrow class of documents that dealt with people who provided the United States with intelligence in war zones. The WikiLeaks databases contain approximately 90,000 Afghanistan War-related significant activity reports, 400,000 Iraq War-related significant activities reports, 800 Guantanamo Bay detainee assessment briefs and 250,000 U.S. Department of State cables, according to prosecutors.

“The department takes seriously the role of journalists in our democracy, and we thank you for it. It is not and never has been the department's policy to target them for reporting," Demers said. "But Julian Assange is no journalist."

“Indeed, no responsible actor, journalist or otherwise, would purposely publish the names of individuals he or she knew to be confidential human sources in war zones," Demers said.

The Justice Department revealed in April that it had filed a criminal case against Assange after Ecuador expelled him from its embassy in London. That charge alleged that he conspired with Manning to crack a password to a military computer where classified information was stored. The case was filed in 2018 but kept secret for more than a year.

The allegations revealed on Thursday were more wide-ranging and more directly related to WikiLeaks' efforts to obtain and publish U.S. government secrets.

Barry Pollack, Assange's lawyer, said it is unprecedented for the government to charge someone under the Espionage Act for encouraging sources to provide truthful information and then publishing it.

"The fig leaf that this is merely about alleged computer hacking has been removed," Pollack said. "These unprecedented charges demonstrate the gravity of the threat the criminal prosecution of Julian Assange poses to all journalists in their endeavor to inform the public about actions that have taken by the U.S. government. "

WikiLeaks tweeted that the case marked the end of national-security journalism.

"This is madness," the group said. "It is the end of national security journalism and the First Amendment."

Nearly all of the new charges against Assange accuse him of violating the Espionage Act, a federal law meant to safeguard defense information. It's unusual for prosecutors to bring such a case against someone who does not work for the government and has not promised to keep its secrets.

The charges include one count of conspiracy to receive national security information, seven counts of obtaining it, nine counts of disclosing it and one count of conspiracy to commit computer intrusion. Prosecutors alleged that Assange also revealed the names of intelligence sources in Afghanistan, China, Iran, Iraq and Syria.

“Assange is alleged to have created grave and imminent risk to their lives and liberty,” Demers said.

“Assange is not charged simply because he was a publisher,” said Zachary Terwilliger, U.S. attorney for the eastern district of Virginia, where the charges against Assange were filed.

Assange was arrested April 11 in London after Ecuador's government ended his seven years of self-imposed exile and expelled him from its London embassy. He is fighting extradition to the United States.

Over four months in 2010, Manning downloaded hundreds of thousands of secret reports on the wars in Iraq and Afghanistan, as well as State Department cables and information about detainees in Guantanamo Bay, Cuba. Manning turned the records over to WikiLeaks, which passed them to journalists and published them on the internet.

Assange had been holed up with political asylum in the Ecuadorian Embassy in London since 2012. After his arrest, he was sentenced in Britain to 50 weeks in jail for jumping bail while facing extradition to Sweden on sexual-assault allegations.

Assange also faces sexual misconduct allegations in Sweden. While one Swedish case of alleged sexual misconduct against Assange was dropped in 2017, when the statute of limitations expired, a rape allegation remains. The statute of limitations in the rape case expires in August 2020. Assange has denied wrongdoing, asserting that the allegations were politically motivated and that the sex was consensual.

More on Julian Assange's legal battles:

Julian Assange, WikiLeaks founder, faces US hacking conspiracy charge

WikiLeaks' Julian Assange given 50-week jail sentence for skipping bail

Sweden requests detention order for Julian Assange