The Australian national currently is in jail in the U.K., where he is serving a 12-month sentence for skipping bail in 2012.
Swedish prosecutors will re-open a rape case against WikiLeaks founder Julian Assange.
The decision leaves Britain facing a decision on whether to extradite him to the Scandinavian country or the United States.
"I have today take the decision to re-open the preliminary investigation," said Eva-Marie Persson, Sweden's deputy director of public prosecutions, on Monday.
The Australian national currently is in jail in the U.K., where he is serving a 12-month sentence for skipping bail in 2012, when he was fighting extradition to Sweden in connection with the same case.
He was arrested by police and carried out of the Ecuadorian Embassy in London, where he sheltered for almost seven years, on April 11.
The U.S. also is seeking the extradition of Assange, 47, so he can face charges relating the release of hundreds of thousands of classified military documents provided by Chelsea Manning.
That means a complex legal fight is certain to take place over his future, potentially involving a lengthy appeal process.
The case was opened following complaints from two Swedish women who said they were the victims of sex crimes committed by Assange. He has denied the allegations, asserting that they were politically motivated and that the sex was consensual.
A police officer who heard the women's accounts decided there was reason to suspect they were victims of sex crimes and handed the case to a prosecutor.
Assange, who describes himself as a journalist, took refuge at the Ecuadorian Embassy in June 2012 to avoid extradition to Sweden.
The statute of limitation on the sexual assault charge expired in 2015 and prosecutors said they were dropping the more serious rape investigation in 2017 due to Assange's unwillingness to leave the Ecuadorian Embassy.
Countries normally process extradition requests in the order they are received and Assange was arrested in relation to the U.S. case on April 11. But it remains in the U.K.'s power to grant any Swedish request first.