WASHINGTON - The Justice Department has prepared an indictment against the WikiLeaks founder, Julian Assange, marking a drastic escalation of the government’s yearslong battle with him and his anti-secrecy group, according to the New York Times.

It was not clear if prosecutors have filed charges against Mr. Assange. The indictment came to light late Thursday through an unrelated court filing in which prosecutors inadvertently mentioned charges against him.

“The court filing was made in error,” said Joshua Stueve, a spokesman for the United States attorney’s office for the Eastern District of Virginia. “That was not the intended name for this filing.”

Mr. Assange has lived for years in the Ecuadorean Embassy in London and would have to be arrested and extradited if he were to face charges in federal court, altogether a multistep diplomatic and legal process.

The disclosure came as the special counsel, Robert S. Mueller III, is investigating links between President Trump’s associates and Russia’s 2016 election interference. WikiLeaks published thousands of emails that year from Democrats during the presidential race that were stolen by Russian intelligence officers. The hackings were a major part of Moscow’s campaign of disruption.

Though the possible charges against Mr. Assange remained a mystery on Thursday, an indictment centering on the publication of information of public interest — even if it was obtained from Russian government hackers — would create a precedent with profound implications for press freedoms.