Lawyers for the US have told the High Court the judge who blocked Julian Assange's extradition was misled by his psychiatrist, APA reports citing BBC.
The United States government is starting a legal appeal to try to get the Wikileaks founder extradited.
In January, a court ruled Mr Assange could not be extradited to the US due to concerns over his mental health.
Mr Assange is wanted over the publication of thousands of classified documents in 2010 and 2011.
The US says the leaks broke the law and endangered lives but Mr Assange says the case is politically motivated.
In the appeal against the January decision, barristers for the US said it had given four clear assurances that he would be treated humanely.
The district judge overseeing the USA's extradition appeal at the start of the year, Vanessa Baraitser, said that while publishing on Wikileaks the classified military and government documents that Mr Assange released arguably amounted to a crime - including the disclosure of the identities of Iraqis and Afghan citizens who had helped coalition forces - he could not be transferred to the US because he was unwell and could take his own life.
However, the US team, launching its appeal, said the evidence was wrong and the Wikileaks founder could even serve a prison sentence back home in Australia.
James Lewis QC, representing the US, told the Lord Chief Justice and Lord Justice Holroyde the conclusion reached in January had been wrong on legal and evidential grounds.
Mr Lewis said Mr Assange's psychiatrist had misled the earlier judge and the US had also not been given an opportunity to answer the judge's concerns.
Mr Assange, 50, is wanted in the US on allegations of a conspiracy to obtain and disclose national defence information following WikiLeaks' publication of hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.
The publications include the release in April 2010 of footage showing US soldiers shooting dead civilians from a helicopter in Iraq.