Julian Assange looks likely to face questioning by Swedish authorities over rape claims, after a court rejected his bid to have an arrest warrant overturned.

The move is set to prolong the six-year long legal stand-off between prosecutors and the Australian.

Mr Assange, 45, is wanted by Swedish authorities for questioning over allegations that he committed rape in 2010 — a claim he denies.

A previous request by Mr Assange to overturn the arrest warrant was denied, but the appeals court then criticised prosecutors for not having done enough to take the investigation forward.

"The Court of Appeal shares the assessment of the District Court that Julian Assange is still suspected on probable cause of rape," the court said.

Assange avoided possible extradition to Sweden by taking refuge in Ecuador's London embassy in 2012, where he still remains.

In August, Ecuadorian officials said they would allow Swedish officials to interview Mr Assange at its embassy.

Earlier this week, Ecuador announced Swedish officials would be able to indirectly question Mr Assange over the rape claims on October 17.

Swedish chief prosecutor Ingrid Isgren and a police investigator will be allowed to be present to ask questions through the Ecuadorian prosecutor, who will later report the findings to Sweden.

Per Samuelson, a Swedish lawyer representing Assange, said he had not yet talked to his client about Friday's verdict.

"I assume we will appeal, it would be strange if we did not," he said.

The court said the lengthy deadlock and the previous passivity of Swedish prosecutors in pursuing the investigation were arguments for setting aside the warrant, but there remained a strong public interest argument for it remaining in place.

"At present, continued detention therefore appears to be both effective and necessary so as to be able to move the investigation forward," the court said.

Mr Assange said he feared further extradition to the United States, where a criminal investigation into the activities of WikiLeaks is ongoing.

Reuters/AFP