Assange, an Australian national, is currently serving a 50-week sentence in Britain for skipping bail after spending seven years holed up in the Ecuadorean embassy in London to avoid extradition to Sweden. He denies the rape accusation.

Sweden wants to question Assange over the allegation, made in 2010, but cannot request his extradition from Britain without a detention order and a European Arrest Warrant.

"Work is now focused on assessing the evidence in the investigation through holding certain complementary interviews," Deputy Director of Public Prosecution Eva-Marie Persson said in a statement.

On June 3, the Uppsala District Court said the investigation could proceed without Assange being ordered detained.

The Swedish prosecutor is working against the clock after reopening the investigation earlier this year following Assange's arrest in Britain.

The statute of limitations for the rape allegation runs out in August 2020 and the prosecutor must decide whether to bring charges before that date.

Furthermore, the United States has already requested Assange's extradition on conspiracy charges and a full hearing will take place in February next year.

Assange, 47, faces 18 counts in the US including conspiring to hack government computers and violating an espionage law. He could spend decades in prison if convicted.

If he were charged and convicted in Sweden, he would face up to four years in prison.

Britain's interior minister will have the final say on whether to extradite Assange to Sweden - if it makes a formal request - or the United States, or neither.

Australian Associated Press