The interview follows years of stalemate since he sought political asylum in Ecuador's London embassy.
Swedish prosecutors had long insisted that Assange should be brought to Stockholm for questioning, but the Australian refused, as Sweden could not guarantee that he would not later be extradited to the United States.
The statute of limitations on lesser charges of sexual assault having already expired, the Swedish authorities have now agreed that the Wikileaks founder be questioned in the embassy by an Ecuadorian prosecutor.
However, the Swedish deputy prosecutor in the case, Ingrid Isgren, was present at the interrogation, together with a Swedish police officer. She arrived just before 11am. A DNA sample might also be taken. A written account of the interview will be given by the Ecuador to the Swedish prosecuting authorities.
Assange's Swedish lawyer Per E Samuelsson raised concerns about the potential quality of the questioning:
“We hope that the interrogation will be of the highest possible quality and that Assange will be able to provide an explanation that will lead to the prosecutors closing the case. If it's low quality we will request a new interrogation.”
Julian Assange was accused of sex attacks on two women during a visit to Sweden in August 2010. A warrant was put out for his arrest, but in 2012 he sought asylum at Ecuador's embassy in London. Lesser charges of sexual assault passed the statute of limitations last year, meaning he can no longer be prosecuted for them. The statute of limitations for the remaining rape accusation will pass in August 2020.
The questioning is expected to take several days.