WikiLeaks is sceptical about reports based on comments from unnamed officials claiming that Assange will not face charges, arguing that it could be a ruse to undermine support for the Australian.
"Anonymous US officials with obscure motivations and unknown authority do not have a good track record in this matter or in any other," WikiLeaks told AAP in a statement.
"It remains to be seen whether the claims by these unknown, anonymous officials are more than just an attempt to reduce public support for WikiLeaks."
The Washington Post has reported that the US Justice Department has "all but concluded" that it won't charge Assange for publishing classified documents because it couldn't do so without also prosecuting news organisations and journalists.
Officials stressed, however, that a formal decision has yet to be made, and a grand jury investigating WikiLeaks remains impanelled.
WikiLeaks said on Tuesday that the fact that the Justice Department has admitted to the continuation of its multimillion-dollar investigation against Assange proves that former Foreign Minister Bob Carr "repeatedly misled the Australian public and parliament when he claimed otherwise".
"It is time for the department and the FBI to do the right thing and finally abandon its absurd persecution of the WikiLeaks organisation and start a full and open inquiry into what has taken place," the website said.
The Washington Post last week quoted US officials as saying that there is not a sealed indictment against Assange.
But the former computer hacker has long maintained that the US has likely issued such a document, as well as a sealed extradition order.
Assange insists he could be arrested by British police and taken to the US if he left Ecuador's diplomatic mission.
The 42-year-old has been holed up in the London embassy for 18 months, avoiding extradition to Sweden over allegations of sexual assault.
He claimed earlier this year that even if the Swedish investigation were dropped, he wouldn't leave for fear of being tried in the US.
Assange wants the British government to guarantee him "safe passage" to South America.
Assange's US lawyer Barry Pollack said the WikiLeaks founder would welcome a "formal unequivocal statement" from Washington that it has not brought charges against him and will not do so in the future.
"Unfortunately, to date, the Department of Justice has not been willing to make such a statement," Pollack told The Guardian.