A UN panel will conclude Wikileaks founder Julian Assange is being "arbitrarily detained" in the UK, the Swedish foreign ministry has said.
Mr Assange, 44, claimed asylum in London's Ecuadorean embassy in 2012. He wants to avoid extradition to Sweden over a rape claim, which he denies.
The Met Police says Mr Assange will be arrested if he leaves the embassy.
Swedish prosecutors said the UN panel's decision would have "no formal impact" on its ongoing investigation.
Mr Assange earlier said his passport should be returned and his arrest warrant dropped if the UN panel, due to deliver its findings on Friday, ruled in his favour.
The Australian was originally arrested in London in 2010 under a European Arrest Warrant issued by Sweden over rape and sexual assault claims.
In 2012, while on bail, he claimed asylum inside the Ecuadorean embassy in Knightsbridge after the UK Supreme Court had ruled the extradition against him could go ahead.
Swedish prosecutors dropped two sex assault claims against Mr Assange last year. However, he still faces the more serious accusation of rape.
'Avoiding lawful arrest'
In 2014, Mr Assange complained to the UN that he was being "arbitrarily detained" as he could not leave the embassy without being arrested.
The application claimed Mr Assange had been "deprived of his liberty in an arbitrary manner for an unacceptable length of time".
The UN's Working Group on Arbitrary Detention has been investigating the issue.
The Press Association said key factors in the panel's decision would include the inability of Mr Assange to access political asylum, the fact he has never been charged, and changes to UK law and procedures since he arrived at the embassy.
Wikileaks earlier tweeted it was waiting for "official confirmation" of the UN panel's decision.
Downing Street said the panel's ruling would not be legally binding in the UK while a European Arrest Warrant remained in place.
"We have been consistently clear that Mr Assange has never been arbitrarily detained by the UK but is, in fact, voluntarily avoiding lawful arrest by choosing to remain in the Ecuadorean embassy," a spokesman said.
"The UK continues to have a legal obligation to extradite Mr Assange to Sweden."
The Swedish foreign ministry said in a statement that it noted the UN panel's decision "differs from that of the Swedish authorities".
The statement added the legal process for Mr Assange's case would be handled in court by Swedish prosecutors.
Per Samuelsson, Mr Assange's lawyer, said Swedish authorities would be "morally" wrong to continue the investigation if the UN panel found in his favour.
"The ball is in Sweden's yard, in the prosecutor's yard. She is not formally bound by the decision by the UN, but morally it is very difficult to go against it."
The journalist John Pilger, who is a friend of Mr Assange, said "the ball is now at the feet of the British government", whose international legal "obligations" were represented by the UN panel.
"They did something in terms of supporting the tribunal in all the other celebrated cases, and Assange now joins them because the UN jurists have clearly found this is a case of arbitrary detention," he said.
Mr Assange's Wikileaks organisation posted secret American government documents on the internet, and he says Washington could seek his extradition to the US to face espionage charges if he is sent to Sweden.
In the statement, published earlier by Wikileaks on Twitter, Mr Assange said: "Should the UN announce tomorrow that I have lost my case against the United Kingdom and Sweden I shall exit the embassy at noon on Friday to accept arrest by British police as there is no meaningful prospect of further appeal.
"However, should I prevail and the state parties be found to have acted unlawfully, I expect the immediate return of my passport and the termination of further attempts to arrest me."
Last October, Scotland Yard said it would no longer station officers outside the Ecuador embassy following an operation which it said had cost £12.6m. But it said "a number of overt and covert tactics to arrest him" would still be deployed.
Julian Assange: Key dates
- August 2010 - Swedish prosecutors issue an arrest warrant for Mr Assange
- May 2012 - UK Supreme Court rules he should be extradited to Sweden to face questioning
- June 2012 - Mr Assange claims asylum in the Ecuadorean embassy in London
- September 2014 - Mr Assange submits complaint against Sweden and the UK to the UN Working Group on Arbitrary Detention
- August 2015 - Swedish prosecutors drop their investigation into two allegations - one of sexual molestation and one of unlawful coercion - but say he still faces the more serious accusation of rape.
- October 2015 - Met Police announce officers will no longer be stationed outside the Ecuadorean embassy