WikiLeaks founder Julian Assange on the balcony of the Ecuadoran Embassy in London in 2017. (Justin Tallis/AFP/Getty Images)

The revelation that WikiLeaks founder Julian Assange has been secretly charged has sparked fears among free-press advocates that the Justice Department is targeting not just those who provide classified information but those who publish it — even as the basic allegations against Assange remain unclear.

The Justice Department under the Trump administration has waged an aggressive crackdown on disclosures of classified information, more than tripling the number of leak investigations in then-Attorney General Jeff Sessions’s first six months on the job.

Assange’s case, though, might mark a dramatic escalation — if prosecutors are essentially charging someone who disseminated information that the government did not want to be made public, free-press advocates say.

“This is troubling because it would mean that the government is bringing criminal charges against a publisher for disclosing leaked, but truthful, information about our government,” said Sonja R. West, a professor of First Amendment law at the University of Georgia Law School.

The devil is in the details, which are largely unknown. Word of the charges against Assange first came in a court filing in an unrelated case that inadvertently referenced the WikiLeaks publisher but offered few specifics.

Assistant U.S. Attorney Kellen S. Dwyer, urging a judge to keep the unrelated matter sealed, wrote that “due to the sophistication of the defendant and the publicity surrounding the case, no other procedure is likely to keep confidential the fact that Assange has been charged.” Later, Dwyer wrote that the charges would “need to remain sealed until Assange is arrested.”

People familiar with the matter told The Washington Post that while the filing was in error — the case was not high profile and had nothing to do with Assange — the information it contained was correct: Assange had been charged.

Joshua Stueve, a spokesman for the U.S. attorney’s office in the Eastern District of Virginia, said: “The court filing was made in error. That was not the intended name for this filing.” Officials otherwise declined to comment on the matter.

On Friday, the Reporters Committee for Freedom of the Press asked a judge to unseal the records about Assange’s case, saying the secrecy surrounding the matter was “anathema to our open system of justice.”

Assange has long been of interest to federal investigators in connection with a wide range of conduct. Federal prosecutors in the Eastern District of Virginia, where the errant filing was made, had been examining the WikiLeaks organization for its 2010 publication of diplomatic cables and military documents.

Justice Department officials in the Obama administration essentially concluded that WikiLeaks was a publisher, and that bringing charges against members of the group might prompt First Amendment challenges or set a dangerous precedent that could invite future prosecutions of traditional news organizations.

Those officials, though, left the investigation open. In the Trump administration, prosecutors had been urged to take a hard look at whether charges could be filed.

WikiLeaks also had come under scrutiny for publishing sensitive CIA cyber-tools in a 2017 leak the group dubbed “Vault 7.” And special counsel Robert S. Mueller III has been exploring the organization’s role in the publication of emails from the Democratic National Committee and the account of Hillary Clinton’s then-campaign chairman, John D. Podesta.

Officials have alleged that the emails were hacked by Russian spies and transferred to WikiLeaks.

It is not clear to which of those matters the charges against Assange relate. Jennifer Robinson, Assange’s lawyer in London, said Friday that the news was “confirmation of what we’ve been concerned about since 2010, that the United States would seek to prosecute Julian Assange for publishing truthful information.”

“This sets a dangerous and chilling precedent for all of the media both in the United States and elsewhere,” she said.

Prosecutors in Assange’s case had contemplated bringing charges under the Espionage Act, among other statutes. Floyd Abrams, an expert in First Amendment law, said the 101-year-old act has long been viewed by press advocates as a “perpetually loaded gun that could too easily be aimed at the press, with ultimately Supreme Court interpretation unpredictable.”

“If it violated the Espionage Act for WikiLeaks to gather information from sources not permitted to release it and then publish it, then what American newspaper could be free from risk?” said Abrams, who practices at Cahill Gordon & Reindel in New York.

It is possible that investigators have gathered evidence that Assange did not act as a mere publisher — but instead actively helped steal information or worked as an agent of a foreign government, legal analysts said. That might distinguish his case in a way that makes it more palatable for prosecutors to pursue, the analysts said.

“I think the big question now is, did the Justice Department find new evidence that would allow them to charge him with some crime, such as conspiracy to hack into computers or some other crime other than just publication, or does the new administration take a different view on whether he can be charged for just publishing classified documents?” said Matthew Miller, a Justice Department spokesman during the Obama administration.

The Justice Department under President Barack Obama was not shy about ferreting out leaks. While Obama was in office, prosecutors brought nine leak cases, more than during all previous administrations combined.

Over time, though, the department took a softer attitude toward such matters. In 2014, then-Attorney General Eric H. Holder Jr. said that as long as he was heading the Justice Department, “no reporter is going to go to jail for doing his or her job.”

At President Trump’s direction, Sessions restored some of the vigor. The former attorney general proudly touted the number of cases the department was investigating.

Barak Cohen, a former prosecutor in the Justice Department’s public-integrity section, said prosecutors generally have to clear higher hurdles when it comes to charging reporters or issuing subpoenas for their records. Cohen, who was involved in the prosecution of former CIA officer Jeffrey Sterling on charges that he leaked classified material to a New York Times reporter, said prosecutors will probably examine to what extent Assange was acting as a journalist to determine if he should be given special consideration.

“The extent to which he is curating the news, or the information that he circulates, has a strong impact on whether or not you consider him a publisher,” Cohen said.

Since June 2012, Assange has been living in the Ecuadoran Embassy in London. He sought asylum there when he was facing possible extradition to Sweden in a sex crimes case, arguing that the case was a pretext for what he predicted would be his arrest and extradition to the United States.

The sex case has since been dropped, but if he left, Assange would still probably be taken into custody for skipping bail. He has faced increasing restrictions on his communications and speech, and people close to him say they suspect that Ecuador has been under considerable pressure from the United States to end his asylum.

If taken into custody, Assange would be able to fight his extradition — a process that in Britain can take years. A spokesman for Britain’s Home Office would not say whether Washington has already applied to bring Assange to the United States.

Karla Adam and Devlin Barrett contributed to this report.