The move sets up a legal battle with the United States, where the Australian computer hacker is separately wanted for allegedly hacking into a Pentagon computer. British authorities will have to decide which extradition request takes precedence.
Assange, who sought refuge in the Ecuadorian Embassy in London in 2012 to avoid being sent to Sweden for questioning, was evicted last month after Ecuador revoked his political asylum. He was arrested by British police on April 11 and is currently in London's Belmarsh Prison serving a 50-week sentence for jumping bail in 2012.
Eva-Marie Persson, Sweden's deputy director of public prosecutions, told a news conference in Stockholm Monday that "there is still a probable cause to suspect that Assange committed a rape." She added: "It is my assessment that a new questioning of Assange is required."