The lawyer acting for WikiLeaks founder Julian Assange over the US criminal investigation into his publication of hundreds of thousands of state secrets has called on the Department of Justice to make a formal statement that it will not prosecute him, in the wake of off-the-record reports that the department is minded not to press charges.

Barry Pollack responded sharply to anonymous officials who told the Washington Post that the US government was unlikely to prosecute Assange because to do so would raise the issue of prosecuting news organisations and journalists involved in the WikiLeaks disclosures. Pollack said that the Justice Department had failed to respond to WikiLeaks’ inquiries about the status of the investigation, which has been led by the eastern district of Virginia, where a grand jury has been impaneled.

“Mr Assange would welcome a formal unequivocal statement from the Department of Justice 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 said.

The Washington Post report is the latest in a flurry of unattributed articles suggesting that the Justice Department is unlikely to take up formal charges against Assange. The paper said that the justice officials had concluded that they had a “New York Times problem” – that is, if they went after Assange they would also have to prosecute journalists from the New York Times, the Guardian and others who worked on the WikiLeaks revelations.

In 2010, WikiLeaks shared with the Guardian and other international news organisations access to the massive trove of US state secrets leaked by the American soldier Chelsea Manning, formerly Bradley. WikiLeaks has consistently argued that it is a journalistic organisation, and thus shielded by the same first amendment protections as any other news outlet.

The Justice Department declined on Tuesday to comment on whether or not it would prosecute Assange.

The drip-drip of anonymous indications from the department of justice that Assange will not be prosecuted, combined with the refusal to make public its intentions, has caused anger and frustration in the WikiLeaks camp which sees it as a form of games-playing on the part of the Obama administration. WikiLeaks used its Twitter feed – often used by Assange as a channel for his personal opinions – to vent a sceptical response to the story, pointing out that the US government under Obama has an aggressive record on pursuing official leaks.

Manning has been sentenced to 35 years in military custody as the source of the WikiLeaks disclosures. She is one of eight individuals charged under the Espionage Act in recent years, the latest being Edward Snowden of the National Security Agency leaks.

Other observers, however, reserved their scepticism for Assange, who has been ensconced for more than a year in the Ecuadorean embassy in London where he has been granted diplomatic asylum. He is wanted for questioning in Sweden in regard to sexual assault allegations.

Assange has said he is resisting extradition to Sweden for fear of being sent in turn to the US to face criminal prosecution over WikiLeaks. Were the US to confirm publicly that it will not press charges, Assange’s critics believe that would undermine his self-defence.

Philip Crowley, the former US State Department spokesperson who resigned from the post in protest at the treatment of Chelsea Manning in a US marine jail, struck that note in a tweet: “With a US indictment not plausible, Julian Assange’s new narrative is information should be free, and rent too.”