WikiLeaks founder says he is disappointed he hasn’t had chance to prove innocence after five-year time limit for bringing some charges expires

Julian Assange has criticised what he described as the incompetence of Sweden’s prosecutor after she dropped her investigation into some of the allegations of sexual assault against him due to the expiration of a five-year time limit for bringing charges.

Prosecutors will continue to pursue an interview with the WikiLeaks founder over an outstanding rape allegation.

“I am extremely disappointed. There was no need for any of this,” Assange said in a statement.

“I am an innocent man. I haven’t even been charged. From the beginning I offered simple solutions. Come to the [Ecuadorian] embassy to take my statement or promise not to send me to the United States. This Swedish official refused both.”

The Swedish prosecutor, Marianne Ny, said she regretted leaving the investigation unfinished, but said she was forced to do so because Assange had refused to leave Ecuador’s London embassy, where he has taken refuge.

Two women made allegations against Assange five years ago in Stockholm, but no charges were brought because the prosecutor was unable to interrogate him after he challenged an extradition order and sought political asylum in the embassy in June 2012.

Assange, who denies the allegations, believes that travelling to Sweden would leave him vulnerable to extradition to the US to face espionage charges. His repeated requests to the Swedish government for a firm guarantee of his safety have been declined.

For more than four years Ny refused to go to London to interview Assange, but changed her mind in March after a Swedish court questioned her failure to make progress in the investigation. Ny cited the impending expiry of the statute of limitations as a reason for the turnabout.

But it was June before the Swedish government made an official request to Ecuador to enter the embassy, and an agreed date to begin interrogation a week later had to be scrapped. After a tense standoff in which each side blamed the other for delays, this week they agreed to formal talks over judicial cooperation, potentially breaking the deadlock – but not in time to prevent the time limit on most of the accusations running out.

“It is still my hope to be able to conduct a hearing [on the rape allegation] since there is an ongoing dialogue on the issue between Sweden and Ecuador,” Ny said in a statement.

Assange said: “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.”

Britain said on Thursday it would make a formal protest to the Ecuadorian government over its decision to provide asylum to Assange.

“Ecuador must recognise that its decision to harbour Mr Assange more than three years ago has prevented the proper course of justice,” the Foreign Office minister Hugo Swire said in a statement.

The statute of limitations for an allegation of unlawful coercion and one case of sexual molestation expired on Thursday; another allegation of sexual molestation expires on Tuesday. The outstanding allegation of rape expires on 17 August 2020.

Claes Borgström, a Stockholm lawyer who represents one of the women whose allegations against Assange will now never be tested in court, said the woman was ambivalent about the situation. “On the one hand, she wanted Assange to face trial and answer for what he has done. On the other, she wants to put this behind her.”

Helena Kennedy QC, a member of Assange’s legal team, said he had spent more time in the embassy than he could ever spend in a Swedish prison, and the remaining allegation against him was “just as unlikely to lead to conviction”.

“The question remains whether we are dealing with incompetence or bad faith or an agenda set by other considerations. I remain unconvinced that this prosecution has been about securing justice for women.”