The Australian activist said a long-awaited interview with the prosecutors fell through in what he labelled a "public relations exercise", although the prosecutor's office declined to comment.
Assange, 43, sought asylum in the embassy in June 2012 to avoid extradition to Sweden, where he faces allegations by two women, one of rape and one of sexual assault, which he denies.
The former computer hacker fears extradition to Sweden could lead to him being transferred to the United States to face trial over WikiLeaks' publication of classified US military and diplomatic documents.
They said they changed their stance because some of the alleged offences will reach their statute of limitations in August.
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Assange condemned what he said was the last minute scrapping of Wednesday's planned interview with prosecutor Marianne Ny.
"To behave in such a way seems reckless and it is hard to imagine that it was more than a public relations exercise," he said in a statement.
According to an email seen by The Guardian newspaper, Ny said the meeting had to be cancelled because she had not received official permission from Quito to enter the embassy.
His 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 has not seen the sun in three years as the embassy has no outdoor area," WikiLeaks said. "His rights have been severely abused."
Entering the embassy meant he jumped his English bail and police have been posted outside since he has been there at a cost of at least 10 million pounds (14 million euros, USD 16 million).