But within 60 days from Thursday, when British police bundled Assange out of the Ecuadorean embassy in London where he had taken refuge seven years ago, US authorities must submit a formal request outlining all the legal charges Assange would face if he is transferred into USA custody.
WikiLeaks tweeted footage of Assange's cat watching his owner being arrested on 11 April.
Ms Massi Fritz said in a text message sent to the Associated Press that "we are going to do everything" to have the Swedish case reopened "so Assange can be extradited to Sweden and prosecuted for rape".
Sweden suspended its investigation of serious sexual misconduct two years ago because Assange was beyond their reach while taking refuge in the Ecuadorian Embassy in London.
Shortly after his arrest, Assange was convicted of breaking his bail, meaning he now faces a possible 12 months in prison and maybe even extradition to the United States, where he could be put on trial for publishing classified information.
Assange, 47, has denied the sexual misconduct allegations, which he claims are politically motivated.
"We expect all the relevant authorities to ensure Mr Assange's right to a fair trial is upheld by authorities, including in any extradition proceedings that may take place", United Nations human rights spokeswoman Ravina Shamdasani told a Geneva news briefing.
British Shadow Home Secretary Diane Abbott said it was right that he should face justice if charges are brought.
After his dramatic arrest, Assange was taken to Westminster Magistrates' Court and found guilty of a British charge of breaching bail.
WikiLeaks founder Julian Assange arrested in London
The UK government welcomed the arrest, which it said was the result of "extensive dialogue" between the UK and Ecuador. Met Police said Assange will be arraigned before Westminster Magistrates' Court "as soon as is possible".
Those charges were dropped in May 2017, but Swedish prosecutors say they are now re-examining the case after a request by one of the alleged victim's lawyers.
However, relations with his Ecuadoran hosts gradually soured and pro-US President Lenin Moreno on Thursday pulled his asylum, cancelled his citizenship and permitted British police to remove Assange.
Assange's lawyer Jennifer Robinson said they would be fighting the extradition request.
They will now re-examine the rape case to decide whether to resume it before the statute of limitations runs out in August 2020.
He could receive up to a year in prison when sentenced at an as yet undetermined later date.
Swedish prosecutors opened an investigation into Assange after two women accused him of sexual offenses during a 2010 visit to Sweden.
"I don't think politicians should be saying he should or should not be. extradited", he said. "From now on we'll be more careful in giving asylum to people who are really worth it, and not miserable hackers whose only goal is to destabilise governments".
"Our priority should be the 2 alleged victims of sexual violence in Sweden & not a ruse to get him extradited to the U.S. as a whistleblower".