Julian Assange isn't about to walk out of the Ecuadorean embassy in London, despite fresh claims by US officials that he's unlikely to face charges for publishing top secret documents.

WikiLeaks is sceptical about the latest report, based on comments from unnamed officials, arguing it could be a ruse to undermine support for the organisation's founder.

"Anonymous US officials with obscure motivations and unknown authority do not have a good track record in this matter or in any other," said WikiLeaks 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" 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 was yet to be taken and a grand jury investigating WikiLeaks remained impanelled.

"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.

'NEW YORK TIMES PROBLEM'

The US Justice Department has all but concluded it will not bring charges against Assange for publishing classified documents because government lawyers say they can't do so without also prosecuting news organisations and journalists, according to US officials.

The officials stressed that a formal decision has not been taken, and a grand jury investigating WikiLeaks remains impanelled, but they said there is little possibility of bringing a case against Assange, unless he is implicated in criminal activity other than releasing online top secret military and diplomatic documents.

The Obama administration has charged government employees and contractors who leak classified information - such as former National Security Agency contractor Edward Snowden and former Army intelligence analyst Bradley Manning - with violations of the Espionage Act. But officials said that although Assange published classified documents, he did not leak them, something they said significantly affects their legal analysis.

"The problem the department has always had in investigating Julian Assange is there is no way to prosecute him for publishing information without the same theory being applied to journalists," said former Justice Department spokesman Matthew Miller.

"And if you are not going to prosecute journalists for publishing classified information, which the department is not, then there is no way to prosecute Assange."

Justice officials said they looked hard at Assange but realised that they have what they described as a "New York Times problem".

If the Justice Department indicted Assange, it would also have to prosecute the New York Times and other news organisations and writers who published classified material, including The Washington Post and Britain's The Guardian, according to the officials, who spoke on condition of anonymity to discuss internal deliberations.

WikiLeaks spokesman Kristinn Hrafnsson said last week that the anti-secrecy organisation is sceptical "short of an open, official, formal confirmation that the US government is not going to prosecute WikiLeaks".

Justice Department officials said it is unclear whether there will be a formal announcement should the grand jury investigation be formally closed.

"We have repeatedly asked the Department of Justice to tell us what the status of the investigation was with respect to Mr Assange," said Barry Pollack, a Washington attorney for Assange.

"They have declined to do so. They have not informed us in any way that they are closing the investigation or have made a decision not to bring charges against Mr Assange. While we would certainly welcome that development, it should not have taken the Department of Justice several years to come to the conclusion that it should not be investigating journalists for publishing truthful information."

There have been persistent rumors that the grand jury investigation of Assange and WikiLeaks had secretly led to charges. Officials said last week there was no sealed indictment, and other officials have since come forward to say, as one senior US official put it, that the department has "all but concluded" it will not bring a case against Assange.

A Justice Department spokesman declined to comment, as did former US attorney Neil MacBride, whose office in the Eastern District of Virginia led the probe into the WikiLeaks organisation.

In an interview with the Post earlier this month, Attorney General Eric Holder said that Justice Department officials are still trying to repatriate Snowden, who has obtained temporary asylum in Russia, to stand trial. But Holder also said that the Justice Department is not planning to prosecute former Guardian reporter Glenn Greenwald, one of the journalists who received documents from Snowden and has written a series of articles based on the leaked material. Greenwald, an American citizen, has said he fears prosecution if returns to the United States from his home in Brazil.

Justice officials said that the same distinction between leaker and journalist or publisher is being made between Manning and Assange. One former law enforcement official said the US government could bring charges against Assange if it discovered a crime, such as evidence that he directly hacked into a US government computer. But the Justice officials said he would almost certainly not be prosecuted for receiving classified material from Manning.

Assange has been living in a room in the Ecuadoran Embassy in London since that country granted him political asylum. Assange is facing sexual assault charges in Sweden. Assange and some of his supporters have said the Australian national fears that if he goes to Sweden to face those charges, he will be extradited to the United States. But current and former US officials dismissed that defence.

"He is hiding out in the embassy to avoid a sexual assault charge in Sweden," Miller said.

- WASHINGTON POST and AAP

"It has nothing to do with the US government."