Prime Minister Julia Gillard needs to clarify reports suggesting that American authorities appear to have secretly established a case against controversial whistleblower Julian Assange, an Australian national.

Assange's anti-secrecy website WikiLeaks has started publishing obtained email exchanges from U.S.-based private intelligence firm Stratfor, which he accused of working against global activist groups apart from its core business of providing strategic information to its corporate and individual clients.

WikiLeaks was a specific target of Stratfor operations, Assange said on Monday.

One of the emails that were exposed, according to Fairfax Media, detailed an alleged declaration made by a senior Stratfor official that states: "We have a sealed indictment on Assange."

Fairfax identified the author of the email as Stratfor vice-president for intelligence Fred Burton, who served in a high-profile position in the U.S. government prior to his stint with Stratfor.

It is widely believed that Burton maintains close ties with his former government colleagues, Fairfax said, giving his declarations high level of credibility, according to Australian Green Senator Scott Ludlam.

In light of the information about Assange's likely prosecution by U.S. authorities, Ludlam called Ms Gillard to categorically state if her government had prior knowledge of the reported intent of the American government to bring up charges against the WikiLeaks founder.

The Greens senator noted that Burton had highlighted the sensitivity of the information, which Fairfax said served as the Stratfor official's reply on concerns about WikiLeaks' decision last year to publish obtained U.S. diplomatic cables that exposed a good amount of operations conducted by the U.S. State Department.

Burton was ranking official of the State Department responsible for intelligence and security matters, according to Fairfax.

And it was almost natural that he would play a major role in the event that the United States would successfully obtain the green light from cooperating governments around the world to allow Assange's prosecution, analysts said.

Ms Gillard needs to tell the Australian public if she had a prior knowledge of the reported plan by the U.S. government to indict Assange, Ludlam said.

"What we need to know is whether the Australian government was tipped off, or whether the Prime Minister read about this ... this morning," the Greens senator was reported by Brisbane Times as saying on Wednesday.

In any case, Ludlam urged the federal government to do what is right in duly protecting an Australian facing pressure and likely prosecution from the most powerful government in the world.

"That we will not permit, and we will not tolerate his transfer to the US, to face charges that could potentially land him in prison, potentially for decades," Ludlam stressed.