WikiLeaks founder Julian Assange cannot be extradited to the United States, a judge has ruled.

Assange, 49, faced an 18-count indictment, alleging a plot to hack computers and a conspiracy to obtain and disclose national defence information.

He has been detained at HMP Belmarsh in Greenwich since his arrest at the Ecuadorian embassy last year.

The case follows WikiLeaks's publication of hundreds of thousands of leaked documents in 2010 and 2011 relating to the Afghanistan and Iraq wars, as well as diplomatic cables.

Assange's fiancee, Stella Moris, with whom he has two young sons, was at the Old Bailey for the hearing on Monday.

District Judge Vanessa Baraitser said: "Faced with the conditions of near total isolation without the protective factors which limited his risk at HMP Belmarsh, I am satisfied the procedures described by the US will not prevent Mr Assange from finding a way to commit suicide and for this reason I have decided extradition would be oppressive by reason of mental harm and I order his discharge."

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Julian Assange wiped his brow after the decision was announced, while his fiancee, Stella Moris, with whom he has two young sons, wept.

She was embraced by Kristinn Hrafnsson, WikiLeaks editor-in-chief, who sat next to her in court as the judgment was delivered.

Prosecutors say Assange helped US defence analyst Chelsea Manning breach the Espionage Act in unlawfully obtaining material, was complicit in hacking by others, and published classified information that put the lives of US informants in danger.

Assange denies plotting with Manning to crack an encrypted password on US Department of Defence computers and says there is no evidence anyone's safety was put at risk.

District Judge Vanessa Baraitser delivered her judgment this morning (January 4) on whether he should be extradited to face the charges in the US.

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Assange's lawyers have said he faces up to 175 years in jail if convicted, although the US government said the sentence was more likely to be between four and six years.

Kristinn Hrafnsson, WikiLeaks editor-in-chief, said: "The mere fact that this case has made it to court let alone gone on this long is an historic, large-scale attack on freedom of speech.

"The US Government should listen to the groundswell of support coming from the mainstream media editorials, NGOs around the world such as Amnesty and Reporters Without Borders and the United Nations who are all calling for these charges to be dropped.

"This is a fight that affects each and every person's right to know and is being fought collectively."

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Assange has been held in high security Belmarsh prison since he was carried out of the Ecuadorian embassy in London by police before being arrested for breaching his bail conditions in April 2019.

He had entered the building in 2012 after exhausting all legal avenues to avoid extradition to Sweden to face sex offence allegations, which he has always denied and were eventually dropped.

The US Government is expected to immediately appeal the ruling.