The father of WikiLeaks founder Julian Assange has said he is worried his son will die in prison after nine years of 'persecution' for daring to reveal US 'war crimes'.

John Shipton told reporters in Geneva he visited his son in a British prison two days ago and needed to 'face the bitter truth' that he 'may die in jail'.

He said: 'This is not the bitter disappointment of a father, this is simply fact.'

Assange used WikiLeaks to publish classified military and diplomatic files in 2010 about US bombing campaigns in Afghanistan and Iraq that proved embarrassing to the US government.

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John Shipton (right) told reporters in Geneva he visited his son (left) in a British prison two days ago and needed to 'face the bitter truth' that he 'may die in jail'

He said: 'This is not the bitter disappointment of a father, this is simply fact.' Pictured: Assange in April after he was arrested

Since then, he has been entangled in a web of judicial proceeding and is currently fighting a US bid to extradite him from Britain on charges filed under the Espionage Act that could land him a sentence of up to 175 years in a US prison.

The 48-year-old whistleblower is being held at a top-security British prison, after police dragged him out of the Ecuadoran embassy in London in April.

He had been holed up in the embassy since 2012 to avoid an extradition order to Sweden - where he was wanted for questioning over accusations of sexual assault, which he has denied.

Mr Shipton said: 'Julian may die in jail over a nine-year persecution for revealing the truth of war crimes.

'It is beyond obscene.'

The 48-year-old whistleblower is currently being held at a top-security British prison

His comments followed a warning from an independent UN rights expert last week that the treatment of Assange was putting his life 'at risk'.

Nils Melzer, the UN special rapporteur on torture and other cruel, inhuman or degrading treatment, said in a statement: 'Unless the UK urgently changes course and alleviates his inhumane situation, Mr Assange's continued exposure to arbitrariness and abuse may soon end up costing his life.'

Melzer, who visited the 48-year-old Australian in a London prison on May 9, nearly a month after his arrest at Ecuador's embassy, has previously warned he was being subjected to drawn-out 'psychological torture'.

Independent UN rights expert Nils Melzer (pictured in 2016) warned in a statement: 'Mr Assange's continued exposure to arbitrariness and abuse may soon end up costing his life'

A spokesman said the independent expert, who does not speak on behalf of the United Nations, had not met Assange since then but had received 'updates' about his condition.

Last Friday's statement warned that Assange's health had continued to deteriorate since his arrest, stressing that 'his life was now at risk.'

In the statement, Melzer pointed out that in May he had demanded immediate measures to protect the WikiLeaks founder's health and dignity.

'However, what we have seen from the UK Government is outright contempt for Mr. Assange's rights and integrity,' he said.

'Despite the medical urgency of my appeal, and the seriousness of the alleged violations, the UK has not undertaken any measures of investigation, prevention and redress required under international law,' he charged.

Assange is pictured in Belmarsh prison, London, in June. Melzer, who visited the 48-year-old Australian in a London prison on May 9, has previously warned he was being subjected to drawn-out 'psychological torture'

Assange 'continues to be detained under oppressive conditions of isolation and surveillance, not justified by his detention status,' he said.

His statement pointed out that Assange had completed his prison sentence for violating his British bail terms in 2012 and was now 'being held exclusively in relation to the pending extradition request from the United States.'

Assange is facing the extradition request by the US over charges he violated the US Espionage Act by publishing a huge cache of military and diplomatic files in 2010.

Julian Assange appeared in court in october ahead of his court battle over his planned extradition to the US

'While the US Government prosecutes Mr. Assange for publishing information about serious human rights violations, including torture and murder, the officials responsible for these crimes continue to enjoy impunity,' Melzer said.

He also decried that 'despite the complexity of the proceedings against him led by the world's most powerful Government, Mr. Assange's access to legal counsel and documents has been severely obstructed.'

This, he said, had effectively undermined 'his most fundamental right to prepare his defence.'

In his appeal, Melzer urged London to bar Assange's extradition to the US, and demanded that 'he be promptly released and allowed to recover his health and rebuild his personal and professional life.'

The statement from Melzer comes weeks after Assange lost the first bout of his extradition battle when a judge rejected his pleas for a full court hearing to be delayed.

The Wikileaks founder appeared in person in court for the first time since May earlier this month after illness prevented him from being at previous hearings in his battle against extradition to the United States to face spying charges.

Assange had raised his fists to his supporters in the public gallery but struggled to say his own name, mumbling, pausing and stuttering as he gave his name and date of birth at the start of the case management hearing.