Assange spoke from snowbound Ellingham Hall, a supporter's 10-bedroom country mansion where he is confined on bail as he fights Sweden's attempt to extradite him on allegations of rape and molestation.
He insisted to television interviewers that he was being subjected to a smear campaign and "what appears to be a secret grand jury investigation against me or our organization."
US Attorney General Eric Holder has said repeatedly that a criminal investigation of the WikiLeaks' continuing release of some 250,000 secret US State Department cables is under way and that anyone found to have broken the law will be held accountable.
The Justice Department has provided no other public comment on who is under investigation or its legal strategy. If pursued, the case could pit the government's efforts to protect sensitive information against press and speech freedoms guaranteed by the US Constitution's First Amendment. The government suspects WikiLeaks received the documents from an Army private, Bradley Manning, who is in the brig on charges of leaking other classified documents to the organization.
Assange did not elaborate on the rumored grand jury investigation, but said he had retained an unspecified US law firm to represent him.
A British High Court judge freed Assange on bail Thursday on condition he reside at the 600-acre estate in eastern England, wear an electronic tag and report to police daily.
Assange spent nine days in prison after handing himself in to British police on Dec. 7. He is wanted in Sweden for questioning about sex allegations leveled against him by two women he spent time with while visiting the country in August.
In an interview Friday on ABC's "Good Morning America," Assange said he had never heard Manning's name until the press began reporting it, though in another interview at Ellingham Hall he appeared close to acknowledging he was one of WikiLeaks' sources.
He called him "a young man somehow embroiled in our publishing activities." "We can see that he's the only person, only one of our military sources, who has been accused," he said.
Assange has also warned of a smear campaign, saying that he expected new allegations about him to surface. It wasn't immediately clear what he was referring to.
