The Swedish prosecutor investigating a rape allegation against WikiLeaks founder Julian Assange said on Monday she had interviewed seven witnesses, including two not previously heard, but had yet to determine how to proceed in the case.

Assange is serving a 50-week sentence in Britain for skipping bail after spending seven years in the Ecuadorean Embassy in London to avoid being extradited to Sweden over a 2010 rape allegation which he denies.

The Swedish prosecutor, Deputy Director of Public Prosecution Eva-Marie Persson, faces a deadline in the case with the statute of limitations set to expire in August 2020.

"We have mainly re-interviewed those individuals who were interviewed in 2010, although two of the persons interviewed have not previously been interviewed," she said in a statement.

"Once we have analyzed the interviews, I will decide how to proceed with the case. The investigation may then be discontinued or I may decide to conduct further inquiries."

If Assange is charged and convicted in Sweden, he could face up to four years in prison. The Australian has said he resisted extradition to Sweden over fears he could later be transported to the United States.

US authorities have requested Assange's extradition on 18 counts, including conspiracy charges and violating an espionage law. He could spend decades in prison if convicted.