"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," former Justice Department spokesman Matthew Miller said.

"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 was sceptical, "short of an open, official, formal confirmation that the US government is not going to prosecute WikiLeaks". Justice Department officials said it was unclear whether there would 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," Barry Pollack, a Washington lawyer for Assange, said. "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."