WikiLeaks founder Julian Assange said it was "increasingly likely" the US would try to extradite him on charges related to leaked cables as he savoured his first day on bail.

Speaking Friday outside ellingham hall, a friend's mansion in eastern England, where he must live while on bail, Mr Assange said he was concerned about potential moves from US authorities.

"The big risk, the risk we have always been concerned about, is onwards extradition to the United States. And that seems to be increasingly serious and increasingly likely," the Australian told reporters.

The 39-year-old founder of the whistle-blowing website is fighting extradition to Sweden, where he is wanted for questioning over allegations that he sexually assaulted two women, which he denies.

But Mr Assange said his lawyers believed a secret US grand jury investigation had been started into his role in WikiLeaks' release of thousands of leaked US diplomatic cables — a probe he condemned as "illegal".

Looking relaxed, he said the mansion was a "big improvement" on the London jail where he was held in solitary confinement for nine days before his release on bail Thursday.

Media reports suggest that US prosecutors are trying to build a case against Mr Assange on the grounds that he encouraged a US soldier, Bradley Manning, to steal US cables from a government computer and pass them to WikiLeaks.

Mr Assange said: "I would say that there is a very aggressive investigation, that a lot of face has been lost by some people, and some people have careers to make by pursuing famous cases."

He said WikiLeaks had pledged 50,000 dollars (38,000 euros) towards Manning's legal fund.

But he told ABC television in the US that "I had never heard of the name Bradley Manning before it was published in the press.

"WikiLeaks technology (was) designed from the very beginning to make sure that we never know the identities or names of people submitting us material."

Meanwhile, the Pentagon defended itself against allegations that Manning was being kept in harsh conditions in a military brig at the Quantico Marine base, Virginia, where he has been placed under a maximum security regimen.

Manning was in solitary confinement because he was considered a national security risk, said prison spokesman First Lieutenant Brian Villiard.

"What I will tell you is that he is not treated any differently than any other maximum confinement detainee," he said.

In interviews with British media, Mr Assange said Manning "is the only one of our military sources who has been accused and that means that he is in a difficult position."

Meanwhile, in Washington a report by congressional researchers said the espionage act and other US laws could be used to prosecute Mr Assange, but there is no known precedent for prosecuting publishers in such a case.

"Leaks of classified information to the press have only rarely been punished as crimes, and we are aware of no case in which a publisher of information obtained through unauthorized disclosure by a government employee has been prosecuted for publishing it," the report said.

On the Swedish case against him, Mr Assange, a former computer hacker, claimed it was part of a "smear campaign" linked to WikiLeaks. But Swedish prosecutors deny their case is related to WikiLeaks.

Mr Assange's supporters have put up a 240,000-pound (283,000-euro, 374,000-dollar) surety to ensure he does not flee the country.

He has also been electronically tagged, is subject to a curfew and must report daily to a police station near the mansion in picturesque Suffolk.

The mansion is owned by Vaughan Smith, a former army officer and journalist who founded the Frontline Club in London, which acts as WikiLeaks' British base.

Mr Assange has vowed the allegations against him will not stop WikiLeaks from releasing further documents.

"People like to present Wikileaks as just me and my backpack it is not true. We're a large organisation," he told reporters Friday.

The latest US cables released by WikiLeaks showed that the former New Zealand Labour Party government led by Helen Clark courted China and France in an attempt to curb American and Australian influence in the Pacific.

They also indicated that Sudanese President Omar al-Bashir siphoned off nine billion dollars (6.79 billion euros) of oil money into British bank accounts.

Meanwhile, according to yet another cable, the Dalai Lama, the exiled Tibetan spiritual leader, said in 2009 the world should focus on climate change in Tibet rather than politics as environmental problems in his Himalayan homeland were more pressing.