London, UK - WikiLeaks founder Julian Assange on Monday won a bid to appeal against a UK court ruling that approved his extradition to the US to face trial for breaking national security laws.

Two London High Court judges granted Assange permission to appeal, having previously asked Washington to provide "satisfactory assurances" about free speech protections at any US trial.

Those submissions were presented at a hearing on Monday, which the 52-year-old Australian did not attend.

Assange is wanted by Washington for publishing hundreds of thousands of secret US documents from 2010 as head of the whistle-blowing website WikiLeaks.

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Had he lost at Monday's hearing, Assange – who has become a figurehead for free speech campaigners – could have been swiftly extradited after a five-year legal battle.

Instead, he will now face another court battle in his long-running legal saga after the UK government approved his extradition in June 2022.

Assange's wife Stella said outside court that the ruling "marks a turning point" and that "we are relieved as a family that the court took the right decision.

"Everyone can see what should be done here. Julian must be freed," she added.

Human rights monitor Amnesty International called the ruling "a rare piece of positive news for Julian Assange and all defenders of press freedom."

"The USA's ongoing attempt to prosecute Assange puts media freedom at risk worldwide. It ridicules the USA's obligations under international law, and their stated commitment to freedom of expression," said Simon Crowther, legal adviser at Amnesty.

In written submissions for the hearing, Edward Fitzgerald, representing Assange, accepted as "unambiguous" US government assurances that he would not face the death penalty.

But he queried whether his client could rely on the First Amendment of the US Constitution, which covers freedom of speech and freedom of the press, at trial.

James Lewis, representing the US government, told the court Assange's conduct was "simply unprotected" by the First Amendment.

It does not apply to anyone "in relation to publication of illegally obtained national defense information giving the names of innocent sources to their grave and imminent risk of harm," he submitted.

Dozens of Assange supporters gathered outside the Royal Courts of Justice in central London early Monday, many wearing t-shirts bearing Assange's face, and cheered as news of the decision filtered through.

"This man's life is at stake," 83-year-old sculptor Jenny West told AFP. "He represents all other journalists, it's a pressing humanitarian situation," she added.

Assange has been detained in the high-security Belmarsh prison in London since April 2019.

He was arrested after spending seven years holed up in Ecuador's London embassy to avoid extradition to Sweden, where he faced accusations of sexual assault that were eventually dropped.

US authorities want to put Assange on trial for divulging US military secrets about the wars in Iraq and Afghanistan.

He is accused of publishing some 700,000 confidential documents relating to US military and diplomatic activities starting in 2010.

The US has accused Assange under the 1917 Espionage Act, which his supporters warn means he could be sentenced to 175 years in prison.

UK courts approved the extradition request after the US vowed that Assange would not go to its most extreme prison, "ADX Florence," nor be subjected to the harsh regime known as "Special Administrative Measures."

His supporters have criticized the legal proceedings he has faced.

"It is abundantly clear of course that the process in the court in the United Kingdom is corrupt. The case is rigged against Julian," Kristinn Hrafnsson, WikiLeaks' editor-in-chief, told reporters last Wednesday.

Assange's supporters say his health is fragile, and the Council of Europe this week voiced concern about his treatment.

The US indicted Assange multiple times between 2018 and 2020, but President Joe Biden has faced domestic and international pressure to drop the case filed under his predecessor Donald Trump.

Biden indicated recently that the US was considering an Australian request to drop the charges.