Swedish prosecutors have dropped a sexual assault investigation against Julian Assange because the time limit on the case had expired.

Some of the allegations against the WikiLeaks founder have reached their statute of limitations after five years.

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

Mr Assange has been holed up at Ecuador's London embassy since 2012 to avoid extradition.

Two of the four allegations against him are reaching their statute of limitations after five years.

The accusations involve one count of sexual assault and another of unlawful coercion.

A separate allegation of sexual molestation will run out on 18 August.

The 44-year-old Australian can still however be prosecuted for the more serious claim of rape.

That carries a ten-year statute of limitations and expires in 2020.

Mr Assange denies the allegations against him, brought by two Swedish women, and insists the sexual encounters were consensual.

Mr Assange said he was "extremely disappointed" with today's announcement.

He said: "There was no need for any of this. I am an innocent man. I haven't even been charged."

"From the beginning I offered simple solutions. Come to the embassy to take my statement or promise not to send me to the United States.

"This Swedish official refused both. She even refused a written statement. Now she has managed to avoid hearing my side of the story entirely.

"This is beyond incompetence. I am strong but the cost to my family is unacceptable.

"Even though I have been improperly treated, I would like to thank the many people in Sweden and the UK who have been very understanding of the wrong which has been done to me and my family."

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

They initially insisted Mr Assange return to Sweden for interrogation.

He rejected that option on fears Stockholm could deliver him to US authorities, who may try him for leaking nearly 750,000 classified military and diplomatic documents in 2010.

In a U-turn in March, prosecutors agreed to Mr Assange's compromise offer to question him inside the London mission.

However, they say they have yet to see their request approved by Ecuador because of procedural issues.

Attorneys for Mr Assange 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," Mr Assange's Swedish lawyer Per Samuelsson said earlier this month.

Claes Borgstrom, a lawyer for one of the two women accusing Mr 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.

Mr Assange has compared living inside the embassy to life on a space station.

His 4.6m by 4m 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.

Meanwhile, Britain has said that it would make a formal protest to Ecuador over its decision to provide asylum to Assange in its London embassy.

British Foreign Office said in a statement: "Ecuador must recognise that its decision to harbour Mr Assange more than three years ago has prevented the proper course of justice".