Julian Assange is currently being questioned over a sexual assault allegation

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A Swedish prosecuting official has arrived at the Ecuadorian embassy in London to be present while Julian Assange is interviewed about a sex allegation in Stockholm.

Ingrid Isgren faced a battery of photographers as she stepped out of a car and walked up the steps to the front door of the embassy in Knightsbridge.

She made no comment and is expected to remain for the duration of the questioning, which is being carried out by an Ecuadorian government official. Sources said the questioning of Assange could take up to three days.

Swedish Chief Prosecutor Ingrid Isgren arrives at the Ecuadorian Embassy
(Frank Augstein/AP)

Assange has been granted political asylum by Ecuador and has been living inside the embassy for more than four years. He believes that if he leaves the embassy he will be extradited to the United States for questioning over the activities of WikiLeaks.

He denies the allegation against him and has been offering to be interviewed at the embassy. Chief prosecutor Isgren has said that providing Assange gives his consent, a DNA sample will also be taken.

The results of the interview will be reported from Ecuador to the Swedish prosecutors in a written statement. After this report, the prosecutors will take a view on the continuation of the investigation.

Banners outside the Ecuadorian embassy in London
(Yui Mok/PA)

A small group of supporters stood opposite the embassy, holding up banners calling for the WikiLeaks founder to be freed.

Swedish police inspector Cecilia Redell, Ecuador ambassador Carlos Ortiz and one of Assange's lawyers, Per Samuelson, were all also present at the embassy for the interview.

A statement on behalf of the Swedish prosecutors said: "As the investigation is ongoing, it is subject to confidentiality. This confidentiality also applies according to Ecuadorian legislation for the investigative measures conducted at the embassy. Therefore, the prosecutors cannot provide information concerning details of the investigation after the interview."

Swedish director of prosecution Marianne Ny, who is responsible for the investigation, said: "I welcome the fact that the investigation can now move forward via an interview with the suspect."