"I can confirm I am leaving the embassy soon, but not for the reason you might think," Assange said at a news conference Monday.
He did not provide additional details but said he is suffering from health problems and would leave "when conditions are right."
However, WikiLeaks said, "his departure is not imminent."
Ecuador's foreign minister, who sat next to him, said his freedom is long overdue.
"The situation must come to an end ... two years is too long," Ricardo Patino said. "It is time to free Julian Assange. It is time for his human rights to be respected."
Swedish authorities want to question him over allegations that he raped one woman and sexually molested another.
He denies the allegations and describes them as politically motivated.
"I've not been charged with an offense in the UK or Sweden," he said Monday.
Patino said Swedish prosecutors have disregarded offers to get evidence from Assange via video conference or send prosecutors to the embassy.
As a result, he said, the case remains unresolved years later, an injustice to both Assange and the two women.
"The end result is these requests have not been heeded," Patino said.
Assange says he fears Sweden will transfer him to the United States, where he could face the death penalty if he is charged and convicted of publishing government secrets through WikiLeaks.
Last month, his lawyers argued that the detention order against him should be revoked.
But Stockholm District Court Judge Lena Egelin ruled that Assange is still suspected, with probable cause, of sex crimes and his detention order should remain in place.
After the decision last month, prosecutor Marianne Ny said the warrant could remain in place until the statute of limitations takes effect -- five years for unlawful coercion and 10 years for rape.
Assange rocketed to international fame when WikiLeaks began publishing secret government documents online.
In addition to the Guantanamo procedures manual, it also published documents related to U.S. activities in Iraq and Afghanistan, and diplomatic cables from U.S. embassies.
In August 2010, Swedish prosecutors issued an arrest warrant for him over allegations of sexual assault from two female WikiLeaks volunteers.
He turned himself in to London authorities the same year, and was remanded in custody.
At the time, a judge ruled that he should be extradited to Sweden, and Assange launched a series of appeals that went all the way to the British Supreme Court. It denied his appeal.
In June 2012, Assange fled to the Ecuadorian Embassy to seek asylum, which was granted in August of the same year.
He's been living at the embassy in London since then.
CNN's Sara Delgrossi, Atika Shubert and Claudia Rebaza contributed to this report.