Lawyers for Julian Assange have asked a court in Sweden to overturn an international arrest warrant for the WikiLeaks founder, who is wanted for questioning in relation to an allegation of rape.
Assange has lived in the Ecuadorian embassy in London since June 2012 after being granted asylum.
It follows a recent ruling by a United Nations panel that his ongoing stay at the embassy amounts to "arbitrary detention".
"We consider that there have arisen a number of new circumstances which mean there is reason to review the earlier decision," Thomas Olsson, one of Assange's lawyers said.
David Cameron says WikiLeaks founder Julian Assange should leave the Ecuadorian embassy and face the allegations of rape against him.Read the full story ›
Emerging onto the balcony of the Ecuadorian Embassy this evening, Julian Assange was holding a copy of the UN tribunal ruling in his favour.
But he still cannot step foot outside the building without being arrested as a warrant remains in place.
Assange's supporters say Britain, Sweden and the USA are complicit in a strategy to ultimately send the Wikileaks founder to America to face investigations for leaking embarrassing State secrets.
ITV News Correspondent, Paul Davies reports:
Wikileaks founder Julian Assange has described a UN ruling, that he has been arbitrarily detained by the UK and Sweden, as a "victory" for himself and the "independence of the UN.
Appearing on the balcony of the Ecuadorian embassy in London, he said that the UN ruling is "legally binding" in response to comments from the Foreign Secretary that he remains a "fugitive of justice".
He added that neither Sweden nor the UK have appealed the decision.
"Having been involved in the exposure in the corruption and war crimes in government for nearly 20 years, it doesn't come as a shock to see the type of injustice that I've been in the business of exposing inflicted on [myself]," he said.
How sweet it is, this is a victory that cannot be denied. It is a victory of historical importance, not just for me, for my family, for my children but the independence of the UN system.
I'm tough, I'm hardened by this process and I can take it. However, what right does this government or the US government or the Swedish government have to deny my children their father for five and a half years without any charges in any country? That is a fact I will never forget.
The Ecuadorian government has demanded WikiLeaks founder Julian Assange be allowed to go free from its London embassy after a UN panel ruled in his favour.
Foreign minister Ricardo Patino said the ruling, which stated Mr Assange has been arbitrarily detained by the UK and Sweden, left both countries with no option but to accept the panel's report, which is not legally binding.
"What more do they want to be accused of before they start to rectify their error?" he told South American broadcaster Telesur.
Mr Patino said Ecuador was analysing its next steps over Mr Assange, who has hailed the ruling as a "significant victory".
Both the UK and Sweden deny Mr Assange has been deprived of his freedom while Swedish prosecutors said the UN panel's decision had no formal impact on its rape investigation against the Australian whistleblower under Swedish law.
WikiLeaks founder Julian Assange hailed the UN working group's ruling that he has been deprived his liberty by the UK and Sweden as "a really significant victory that has brought a smile to my face".
Addressing reporters at a press conference via video from inside the Ecuadorian embassy, Mr Assange said the ruling in his favour is the "end of the road" for the legal arguments put forward by the two countries.
"Put simply, those arguments lost," Mr Assange said. "There is no appeal. The time for appeal is over."
He attacked the Foreign Office's rejection of the panel's decision as insulting and said it was a matter for the UN to enforce its decisions.
A five-person panel became four before even looking at the Assange case and ended with the group divided and ridiculed by Philip Hammond.Read the full story ›
Foreign Secretary Philip Hammond has described the UN working group's report on Julian Assange "ridiculous" and said the WikiLeaks founder is a "fugitive from justice".
The UN panel ruled Mr Assange is being "arbitrarily detained" in the Ecuadorian embassy in London and called for him to be paid compensation.
But Mr Hammond said the panel lacked credibility.
I reject the decision of this working group. It is a group made up of lay people and not lawyers. Julian Assange is a fugitive from justice. He is hiding from justice in the Ecuadorian embassy.
He can come out any time he chooses... But he will have to face justice in Sweden if he chooses to do so. This is frankly a ridiculous finding by the working group and we reject it.
From his 2010 arrest warrant to a UN expert panel's call for the WikiLeaks founder to be freed, review the key dates in the Assange case.Read the full story ›
The Foreign Office "completely rejects" Julian Assange is the victim of arbitrary detention and will formally contest the ruling by the UN's panel.
The WikiLeaks founder is wanted for extradition on a rape accusation in Sweden and has lived in the embassy since June 2012.
A Foreign Office spokesperson said the UN working group's decision against the UK and Sweden "changes nothing" in relation to the case.
Julian Assange has never been arbitrarily detained by the UK. The opinion of the UN Working Group ignores the facts and the well-recognised protections of the British legal system. He is, in fact, voluntarily avoiding lawful arrest by choosing to remain in the Ecuadorean embassy. An allegation of rape is still outstanding and a European Arrest Warrant in place, so the UK continues to have a legal obligation to extradite him to Sweden. As the UK is not a party to the Caracas Convention, we do not recognise ‘diplomatic asylum’.
We are deeply frustrated that this unacceptable situation is still being allowed to continue. Ecuador must engage with Sweden in good faith to bring it to an end. Americas Minister Hugo Swire made this clear to the Ecuadorean Ambassador in November, and we continue to raise the matter in Quito.
The Metropolitan Police have said they will make "every effort" to arrest Mr Assange should he leave the embassy.