Ecuador responded that Sweden's and Britain's "inaction" was why Assange had not been questioned by prosecutors before the statute of limitations on three of the accusations against him expired.
Swedish officials on Thursday confirmed that investigations into two claims of sexual molestation and one of unlawful coercion were being dropped as two had reached their time limit and a third would do so next Tuesday.
But prosecutors say they still hope to question Assange on an allegation of rape that doesn't expire until 2020.
Two women in Sweden made the 2010 sex claims, which Assange strongly denies.
Assange fought extradition to Sweden from Britain on fears he would be handed over to the United States over secret documents published by his whistleblowing organisation.
In a statement, Assange said he was extremely disappointed as he was an innocent man who hadn't 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.
A statement from Ny's office said: "Julian Assange, on his own accord, has evaded prosecution by seeking refuge in the embassy of Ecuador.
"As the statute of limitation has run [out] on some of the crimes, I am compelled to discontinue the investigation with respect to these crimes."
The statement added that a Swedish request to interview Assange at the Ecuadorian embassy was submitted at the beginning of June, "but a permission has yet to be received".
"I still hope, however, that I will be able to arrange for an interview, as there are ongoing negotiations between Sweden and Ecuador," Ny said.
Yesterday, Britain's Minister of State for Foreign and Commonwealth Affairs Hugo Swire called the harbouring of Assange in the Ecuadorian embassy an "abuse of diplomatic relations" and a "growing stain" on Ecuador's reputation.
"Ecuador must recognise that its decision to harbour Mr Assange more than three years ago has prevented the proper course of justice," he said.
"As a result, some of the serious sexual allegations against him will now expire."
But the Ecuadoran Foreign Ministry said the cause of the impasse was the "continued inaction by British and Swedish authorities for the nearly 1000 days of his stay in the embassy".
"During that time, the Ecuadoran Foreign Ministry's proposals and calls for dialogue have fallen on deaf ears," it said.
- AAP
