WikiLeaks founder Julian Assange has asked his father to move to the UK during an emotional prison visit.
The 47-year-old is poised to move out of the medical ward of London's Belmarsh prison and on Tuesday shared a moving hug with father John Shipton, who he has not seen since Christmas.
WikiLeaks founder Julian Assange, 47, is facing an 18-count indictment in the United States. Source: AAP
It comes as the US government has formally submitted an extradition request to the UK for Mr Assange, according to a US official.
The United States will detail all the charges against Mr Assange when it seeks his extradition in a London court on Friday, the editor of the whistleblowers' website said.
"The American authorities, the Department of Justice, will present the evidence in support of their extradition demand," Kristinn Hrafnsson told reporters.
The US Justice Department confirmed on Tuesday that it had submitted a formal extradition request.
The 47-year-old Australian is not expected to attend Friday's hearing but could take part from prison via video link, although it will be largely procedural.
The "first real confrontation of arguments" in court will not be for several weeks or months, Ms Hrafnsson said.
Mr Assange faces an 18-count indictment that accuses him of soliciting and publishing classified information and of conspiring with former Army private Chelsea Manning to crack a Defence Department computer password.
The 47-year-old Assange was evicted on 11 April from the Ecuadorian Embassy in London, where he had been holed up since 2012 after Ecuador granted him political asylum.
He was arrested by British police and is currently serving a 50-week sentence for jumping bail in 2012.
Sweden also seeks him for questioning about an alleged rape, which Mr Assange has denied.
The US official spoke on condition of anonymity.
Mr Shipton was joined by Chinese artist and activist Ai Weiwei for the visit at the high security jail.
But Mr Shipton told reporters outside Belmarsh that his son's weight has "stabilised", and that he expects to be moved back in the prison population in the next day or so.
Mr Assange is serving a 50-week prison sentence after being dragged out of the Ecuadorian embassy in April and jailed for a bail violation.
"It was just very moving to see Julian, particularly in those circumstances, coming out of sick bay and having lost 10kg weight," said Mr Shipton, 74.
He said he shared a hug with his son which he described as "not a hug that you want to end".
Mr Shipton said Mr Assange asked him to move from Melbourne to the UK and he replied "yes, I'll be here in August".
"His movements have become fine and delicate, and he thinks through things carefully before he says them, so he doesn't speak quickly like I am now," Mr Shipton said, adding that his son had not lost his spirit.
"The spark is there. The fight is there. Just the fire's a little banked."
An emotional Mr Shipton described his son as "a gentle intellectual" and said he was was moved to the sick bay due to weight loss.
Ai Weiwei said Mr Assange, who was recently visited at Belmarsh by Pamela Anderson, is "under psychological stress and pressure", adding that he was "very happy" to see his visitors.
Artist Ai Weiwei speaks to the media after visiting WikiLeaks founder Julian Assange at HMP Belmarsh, in London. Source: AAP
Asked if he thinks Mr Assange remains optimistic about his future, the artist said: "No I don't think so. I think he's deeply worried."
An investigation has been reopened into an allegation of rape in Sweden, which Mr Assange has always denied.
He also faces an extradition request from the US on allegations of spying.
The US Justice Department indicted Mr Assange on 18 counts.
He is accused of working with former US army intelligence analyst Chelsea Manning in "unlawfully obtaining and disclosing classified documents related to the national defence", a statement said.
