Assange has lived in the Ecuadorian Embassy in London since 2012, in order to avoid extradition to Sweden over the allegation, which he denies. He has been there ever since, fearing that if he is arrested he might ultimately be extradited to the United States.
The preliminary investigation on Assange, 44, was opened in 2010.
"We are not making a statement about his guilt", Ny said, adding that the investigation could be reopened if Assange came to Sweden before the statute of limitations deadline for the rape allegation in 2020.
In the meantime, in Britain, police have said Assange is still wanted for jumping bail and will face arrest if he leaves Ecuadorean embassy in London.
Chelsea Manning was released from prison on Wednesday after serving seven years of her 35-year sentence, which was commuted by Barack Obama as one of his final acts as President.More news: FedEx confirms it was hit by global malware attack
"Westminster Magistrates' Court issued a warrant for the arrest of Julian Assange following him failing to surrender to the court on the 29 June 2012", a statement said.
WikiLeaks said on Twitter that the ball was now in the UK's court.
After the news was announced, WikiLeaks tweeted that the "focus now moves to the UK", saying the country had "refused to confirm or deny whether it has already received a USA extradition warrant for Julian Assange". But Assange later wrote on Twitter that he would "not forgive or forget".
Four hours later, he tweeted: "Detained for 7 years without charge by while my children grew up and my name was slandered".
However, it noted that now the Swedish authorities had dropped their investigation, Assange was "wanted for a much less serious offence" than before and said the force would "provide a level of resourcing which is proportionate to that offence". "My client is shocked and no decision to (end the case) can make her change that Assange exposed her to rape".