London’s High Court has cleared the way for Julian Assange to be extradited to the USA where he faces espionage charges relating to the publication of thousands of leaked documents in 2010 and 2011.

Judges ruled the 50-year-old could be handed over to America after the US appealed an earlier UK court decision that he should not be extradited because he would likely commit suicide in jail.

Justice Timothy Holroyde said he was satisfied with a package of assurances given by the United States about the conditions of the WikiLeaks founder’s detention.

These included pledges not to hold him in a so-called “ADX” maximum security prison and that he would be transferred to Australia to serve his sentence if convicted.

Assange’s fiancee Stella Morris has declared his legal team would appeal the latest decision “at the earliest possible moment”, saying Julian represented “all our liberties and all our rights”.

The legal wrangling is likely to go to the Supreme Court, the final court of appeal.

“For the past… two years and a half, Julian has remained in Belmarsh prison, and in fact he has been detained since 7 December 2010 in one form or another, 11 years. For how long can this go on?” said Ms Morris.

“How can it be fair, how can it be right, how can it be possible, to extradite Julian to the very country which plotted to kill him?

“We will appeal this decision at the earliest possible moment.”

If Assange’s lawyers do take his case to the Supreme Court, justices will first decide whether to hear the case before any appeal is heard.

US authorities accuse Australian-born Assange of 18 counts relating to WikiLeaks’ release of vast troves of confidential US military records and diplomatic cables which they said had put lives in danger.

His supporters cast Assange as an anti-establishment hero who has been victimised for exposing US wrongdoing in Afghanistan and Iraq.

He could face 175 years in prison however the US said in its appeal the sentence was likely to be between three and six years.

Justice Holroyde said the case must now be remitted to Westminster Magistrates Court with the direction that judges send it to the British government to decide whether or not Assange should be extradited.

Assange, who denies any wrongdoing, was not in court.

He remains in London’s high-security Belmarsh prison, where he has been for more than two-and-a-half years after he was carried out of the Ecuadorian embassy by police before being arrested for breaching his bail conditions.

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

US authorities brought the High Court challenge against a January ruling by then-district judge Vanessa Baraitser that Assange should not be sent to the US, in which she cited a real and “oppressive” risk of suicide.

After a two-day hearing in October, the Lord Chief Justice Lord Burnett, sitting with Lord Justice Holroyde, ruled in favour of the US on Friday (local time).

Supporters of Assange gathered outside of the court after the ruling, chanting “free Julian Assange” and “no extradition”.

They tied hundreds of yellow ribbons to the court’s gates and held up placards saying “journalism is not a crime”.

WikiLeaks came to international prominence when it published a US military video in 2010 showing a 2007 attack by Apache helicopters in Baghdad that killed a dozen people, including two Reuters news staff.

It then released thousands of secret classified files and diplomatic cables.

US prosecutors and security officials regard Assange as a reckless and dangerous enemy of the state whose actions imperilled the lives of agents named in the leaked material.

His admirers have hailed Assange as a hero for exposing what they describe as abuse of power by modern states and for championing free speech.

-with AAP