Julian Assange revealed his health is worsening and said 'I'm slowly dying here' in a slurred phone call from prison on Christmas Eve, it has been claimed.

The Wikileaks founder, who is currently being held in Belmarsh Prison, south east London, revealed the news in a call with his journalist friend Vaughan Smith.

Assange, 48, stayed with the free speech supporter, 56, at Ellingham Hall, Norfolk between 2010 and 2011 after he was released on conditional bail on allegations of rape in Stockholm and the two have remained in touch.

Assange later sought refuge in the Ecuadorian embassy in London but was jailed for 50 weeks in May for breaching his bail conditions after going into hiding to avoid extradition to Sweden over sex offence allegations, which he has always denied.

Since being locked up concern has been raised over his health, with Smith now claiming Assange had trouble speaking and appeared to be drugged in his one permitted phone call over the Christmas period.

Julian Assange is currently fighting extradition to the US where he would stand trial for conspiring with army intelligence analyst Chelsea Manning to expose military secrets between January and May 2010 (pictured being whisked back to maximum-security Belmarsh Prison in southeast London on December 20)

Assange, 48, stayed with Vaughan Smith, 56, at Ellingham Hall, Norfolk between 2010 and 2011 after he was released on conditional bail on allegations of rape in Stockholm and the two have remained in touch

The journalist told RT that Assange's 'speech was slurred' and that he was 'speaking slowly'. He added: 'Julian is highly articulate, a very clear person when he speaks. And he sounded awful… it was very upsetting to hear him'.

The news comes weeks after more than 60 doctors warned in an open letter addressed to Home Secretary Priti Patel that Assange could die in prison without urgent medical care.

The medics, from the UK, Australia, Europe and Sri Lanka, expressed 'serious concerns' about Assange's fitness to stand trial.

He is currently fighting extradition to the US where he would stand trial for conspiring with army intelligence analyst Chelsea Manning to expose military secrets between January and May 2010.

His full extradition hearing will be heard at Belmarsh Magistrates' Court on February 24 next year and will last up to four weeks.

There will be a brief administrative hearing back at Westminster Magistrates' Court on 18 January.

Assange was jailed for 50 weeks in May for breaching his bail conditions after going into hiding to avoid extradition to Sweden over sex offence allegations, which he has always denied (pictured, Belmarsh Prison where Assange is currently being held)

Assange was jailed for 50 weeks in May for breaching his bail conditions after going into hiding in the Ecuadorian embassy in London to avoid extradition to Sweden over sex offence allegations, which he has always denied.

Last month, WikiLeaks welcomed a decision by the Swedish authorities to drop a rape investigation.

Assange has been in custody since he was dramatically removed from the embassy building in April, and at a hearing in October appeared to struggle to say his own name, telling Westminster Magistrates' Court: 'I can't think properly.'

Recently, Assange's close friend Pamela Anderson claimed she was threatened by a prison warden at Belmarsh.

Anderson said that towards the end of her meeting with Assange at Belmarsh high security prison in London in May the warden 'stormed in'.

She said: 'The warden stormed in and made it very clear to me, that if I were going to be a problem - he'd make problems for Julian. It was a direct threat.'

It was unclear why the warden, who is known as the prison governor in the UK, might have believed Anderson was going to cause trouble.

A UK Prison Service spokesman said: 'The Governor of HMP Belmarsh did not threaten Ms Anderson or Mr Assange.'

On November 25, Home Secretary Priti Patel received a letter from medics across the world which stated Assange 'could die' at Belmarsh if he didn't receive 'urgent medical care'.

The medics - from the UK, Australia, Europe and Sri Lanka - express 'serious concerns' about the 48-year-old's health.

Julian Assange arriving at Westminster Magistrates' Court in London in April this year

The doctors are calling for Assange to be transferred to a university teaching hospital, where he can be assessed and treated by an expert medical team.

The letter, which has also been copied to shadow home secretary Diane Abbott, says: 'From a medical point of view, on the evidence currently available, we have serious concerns about Mr Assange's fitness to stand trial in February 2020.

'Most importantly, it is our opinion that Mr Assange requires urgent expert medical assessment of both his physical and psychological state of health.

'Any medical treatment indicated should be administered in a properly equipped and expertly staffed university teaching hospital (tertiary care).

'Were such urgent assessment and treatment not to take place, we have real concerns, on the evidence currently available, that Mr Assange could die in prison.

'The medical situation is thereby urgent. There is no time to lose.'

Julian Assange pictured as he is led out of the Ecuadorian Embassy in London in handcuffs following his sensational arrest by British police earlier this year

Dr Lissa Johnson, a clinical psychologist in Australia and one of the letter's signatories, said: 'Given the rapid decline of his health in Belmarsh prison, Julian Assange must immediately be transferred to a university teaching hospital for appropriate and specialised medical care.

'If the UK Government fails to heed doctors' advice by urgently arranging such a transfer on medical grounds, there is a very real possibility that Mr Assange may die.

'As it stands, serious questions surround not only the health impacts of Mr Assange's detention conditions, but his medical fitness to stand trial and prepare his defence.

'Independent specialist medical assessment is therefore needed to determine whether Julian Assange is medically fit for any of his pending legal proceedings.

'Consistent with its commitment to human rights and rule of law, the UK Government must heed the urgent warning of medical professionals from around the world, and transfer Julian Assange to an appropriately specialised and expert hospital setting, before it's too late.'