London (AFP) - Prosecutors were questioning WikiLeaks founder Julian Assange at the Ecuadoran embassy in London on Monday, the latest twist in the long-running legal battle over a rape allegation against him.

Swedish prosecutor Ingrid Isgren, due to be present while Assange faced a grilling by an Ecuadoran prosecutor, entered the embassy behind the famous Harrods department store shortly before 1000 GMT, an AFP photographer said.

Assange's lawyer Per Samuelsson said the questioning is expected to last several days at the embassy where the founder of the secret-spilling website has been holed up for four years, refusing to come out over fears he could be extradited to the United States.

"I am very hopeful," Samuelsson told Sweden's TT news agency. "Objectively, there is no doubt that everything happened as Assange said it did."

Assange, a 45-year-old Australian, sought refuge in the embassy in June 2012 after Sweden sought his arrest over allegations of rape and sexual assault. He has always denied the claims, saying they were politically motivated.

The former computer hacker insists his sexual encounters with the two women, who he met on a 2010 trip to Sweden, were consensual.

He has refused to travel to Sweden for questioning, fearing he could be extradited over WikiLeaks' explosive release of 500,000 US secret military files on the wars in Afghanistan and Iraq.

Swedish prosecutors dropped the sexual assault probe last year after the five-year statute of limitations expired.

But they still want to question him about the 2010 rape allegation, which carries a 10-year statute of limitations.

- 'Time for a trial' -

A small group of protesters gathered outside the embassy to greet the prosecutors, waving banners reading "Free Assange" and "You Won't Stop WikiLeaks".

"Freedom Loving People of the World Say Thank You Ecuador!" read another banner hung under the balcony from which Assange has sometimes addressed supporters.

But Elisabeth Fritz, the lawyer for Assange's alleged victim, said: "My client has been waiting six years for justice... It is time for this to go to trial."

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She added in a statement: "We are expecting that the prosecutor will announce charges after this questioning and that these charges lead to a trial in a Swedish court."

A Swedish police inspector was also due to attend the questioning and investigators planned to take a DNA sample from Assange, subject to his agreement.

The grilling has been delayed in the past because of diplomatic disagreements between Ecuador and Sweden, making this the first time Assange has been interviewed over the matter since initial questioning by Swedish police at the time of the allegation.

Speaking through his lawyer, Assange has said he welcomes the "chance to clear his name" and hopes the investigation will subsequently close.

In May, a Swedish court reaffirmed the arrest order, rejecting the finding of a UN working group that his confinement in the Ecuadoran embassy amounted to arbitrary detention.

- Petition for Trump 'pardon' -

In the days since the US election, supporters have launched a petition calling on President-elect Donald Trump to pardon Assange by "absolving him of any crimes alleged against him" -- an apparent reference to the military leaks.

The petition on the change.org website, which has gathered more than 17,700 signatures, hails Assange as a "hero" for exposing the "corruption of those who presume to rule us".

Assange's lawyer said he had made "repeated requests" for an interview with police to address the rape claim, though Ecuadoran prosecutors say a hearing scheduled for October was postponed at the Australian's request.

"Julian Assange has always wanted to tell his version to the Swedish police. He wants a chance to clear his name," Samuelsson told AFP.

Later on Monday WikiLeaks said Samuelsson had not been summoned to attend Assange's questioning, blaming Sweden for "irregularities with procedure".

"For the first time since August 2010, Mr. Assange was finally able to give his statement in relation to this allegation.

"He has done so in part to ensure the Swedish authorities have no further excuse not to discontinue their preliminary investigation," WikiLeaks said in a statement, adding that Assange fully cooperated with the process.

The grilling comes after WikiLeaks returned to the spotlight with the leak of tens of thousands of emails from the US Democratic Party and presidential candidate Hillary Clinton's campaign in the final weeks of the race for the White House.

Assange defended the publication, denying links with Russia and claims that his website was trying to influence the US vote which saw Trump defeat Clinton in a stunning upset.

Tensions with his Ecuadoran hosts have been growing, with the Clinton leaks prompting the embassy to cut Assange's internet access, citing respect for "non-intervention" in the affairs of other states.