Swedish prosecutors said on Thursday they had dropped a sexual assault probe against Julian Assange because the time limit on the case had expired.

Two of the four allegations against the WikiLeaks founder — who has been holed up at Ecuador's London embassy since 2012 to avoid extradition — have reached their statute of limitations after five years.

"Now that the statue of limitations has expired on certain offenses, I am obliged to drop part of the investigation," prosecutor Marianne Ny said.

However she said she still wanted to question the 44-year-old Australian over a more serious claim of rape.

The accusations dropped involve one count of sexual assault and another of unlawful coercion. A separate allegation of sexual molestation will run out on Aug. 18.

The Australian can still however be prosecuted for rape, which carries a 10-year statute of limitations and expires in 2020.

Assange has always denied the allegations brought by two Swedish women, and insists the sexual encounters were consensual.

Under Swedish law, if a suspect is not questioned before the deadline expires, they can no longer be tried for the alleged crimes.

Despite repeated attempts, prosecutors have been unable to gain access to Ecuador's embassy.

They initially insisted Assange return to Sweden for interrogation — a condition he rejected on fears Stockholm could deliver him to U.S. authorities, who may try him for leaking nearly 750,000 classified military and diplomatic documents in 2010.

In an about-face in March, prosecutors agreed to Assange's compromise offer to question him inside the London mission, but say they have yet to see their request approved by Ecuador because of procedural issues — leading critics to suspect Quito of playing the clock.

Attorneys for Assange, however, say suspicions that Ecuador is using delaying tactics are unfounded.

"The (Swedish) request came in late and is being processed by Ecuador, which will certainly approve it after following its own procedures," Assange's Swedish lawyer Per Samuelsson told AFP earlier this month.

Claes Borgstrom, a lawyer for one of the two women accusing Assange of having assaulted them in 2010, said his client was trying to come to terms with the likelihood that the case will never be tried.

"She has always been ready to stand by her accusations and wanted to bring the case to court. But at the same time a weight has been lifted. This has been dragging on for five years and she wants to go back to her normal life," he told the daily Dagens Nyheter earlier this week.

Assange has compared living inside the embassy — which has no garden but is in the plush Knightsbridge district, near Harrods department store — to life on a space station.

His 15-feet by 13-feet (4.5- by 4-meter) room is divided into an office and a living area. He has a treadmill, shower, microwave and sun lamp, and spends most of his day at his computer.

He is subject to a European arrest warrant and Britain has vowed to detain him if he sets foot outside the embassy, which is under constant police surveillance.