The Swedish investigation has been reopened at the request of the alleged victim.
This month, Assange told a British court that he would not consent to being extradited to the US, where he is wanted on a charge of conspiring with a former Army intelligence analyst Chelsea Manning to hack a Defence Department computer. US officials have been investigating Assange and Manning for their roles in the release of classified military and diplomatic documents in 2010.
The US government is expected to outline its formal case for extradition in a British court next month.
If Sweden does seek to extradite Assange - a logical step if it wants to move forward with the rape investigation - Britain would face two competing extradition requests. It would be up to Britain's Home Secretary to decide which request, if either, to prioritise.
Extradition experts said that decision would likely rest on factors such as the gravity of the allegations, the chronology of events and which extradition request came first.
Rebecca Niblock, an extradition lawyer with the London-based firm Kingsley Napley, said the Swedish case would likely take precedence over the US one. "It would be very difficult politically to say that a computer intrusion offence is more serious than an allegation of rape," she said.
If Assange were extradited to Sweden, then the US could still pursue an extradition request with Swedish authorities. In that scenario, Britain would have to give consent.
Persson, the Swedish prosecutor, said that following Assange's arrest last month in London, "the circumstances in this case have changed".
She said that according to information received from British authorities, Assange will "serve 25 weeks of his sentence before he can be released."
She added: "I am well aware of the fact that an extradition process is ongoing in the UK and that he could be extradited to the US In the event of a conflict between a European arrest warrant and a request for extradition from the US, UK authorities will decide on the order of priority. The outcome of this process is impossible to predict."
Swedish prosecutors argued that time is of essence in their case, because the statute of limitations in the rape case expires in August 2020.
Following a trip to Stockholm in August 2010, Assange was accused of sexual misconduct by two Swedish women. Assange denied the claims, saying the sex was consensual.
In 2015, Swedish prosecutors dropped their probe into some of the allegations - sexual molestation and unlawful coercion - because of the statue of limitations had expired, but they continued their investigation into an allegation of rape.
WikiLeaks editor Kristinn Hrafnsson said reopening the Swedish case would give Assange "a chance to clear his name".
Elisabeth Massi Fritz, the lawyer for Assange's accuser, told a news conference in Stockholm that her client is "very hopeful about getting restitution, and we both hope that justice will win".
