Julian Assange makes his way back indoors after speaking to the media from the balcony of the Embassy Of Ecuador on May 19, 2017.
U.S. Attorney Kellen Dwyer filed a motion to seal a criminal complaint in a sex crime case in August.
Assange and his supporters have periodically said U.S. authorities had filed secret criminal charges against him, an assertion against which some United States officials pushed back until recently.
The US justice department confirmed the filing was made in error, while WikiLeaks said it was the result of a "cut and paste" mistake.
The prosecutor added that the charges would "need to remain sealed until Assange is arrested".
The accident was first reported on Twitter by Seamus Hughes, deputy director of the Program on Extremism at George Washington University, and confirmed by The Washington Post. He is known to follow court filings closely. Some of President Donald Trump's associates, including former strategist Roger Stone, face questioning in special counsel Robert Mueller's investigation over their potential ties to WikiLeaks.
"That was not the intended name for this filing", he told The Washington Post.
"The last thing the Department of Justice should be doing is pursuing criminal charges against someone for publishing truthful information", he said. The reports did not indicate what charges Assange will face. If the Justice Department indicted Assange, it would also have to prosecute the New York Times and other news organizations and writers who published classified material, including The Washington Post and Britain's Guardian newspaper.
US officials have previously acknowledged that federal prosecutors based in Alexandria have been conducting a lengthy criminal investigation into WikiLeaks and its founder. It's unclear what charges may be brought against Assange; the Justice Department has previously considered prosecuting him over his role in the release of hacked DNC emails during the 2016 presidential campaign, as well as over the release of the so-called Iraq and Afghanistan War Logs, shared by US military whistleblower Chelsea Manning.
USA officials had no comment on the disclosure in the document about a sealed indictment of Assange.
The 47-year-old has always denied the allegations, and his supporters claim the accusations were an attempt to possibly extradite him to the United States, where he could face charges over WikiLeaks' publication of classified military and diplomatic documents.
If Assange were to leave the embassy and be arrested by British authorities, he would likely still fight extradition in the British courts.