Ecuador's foreign minister, María Fernanda Espinosa, said her country was now seeking a "third country or a personality" to mediate a settlement with the United Kingdom to resolve the impasse and said it was "considering and exploring the possibility of mediation".
Assange has been living in Ecuador's embassy in the affluent borough of Knightsbridge since 2012, initially to avoid extradition to Sweden over rape charges.
Sweden dropped their investigation over the 2010 allegations a year ago, but British police have said they are still seeking to arrest him for failing to surrender to a court after violating bail terms. The Foreign Office said in a statement the only way for the embassy to resolve Assange's issue would be for him to leave its premises and face justice.
The 46-year-old Australian still fears being sent to the United States to face charges over WikiLeaks' release of secret U.S. government documents.
Assange had been wanted on assault claims in Sweden, but that case against him has been dropped.More news: Iran nuclear pact 'essential' - EU's message to America
'The UK did not grant that request, nor are we in talks with Ecuador on this matter. Shortly before the 2016 U.S. election, WikiLeaks accused Ecuadorian officials in the London embassy of temporarily cutting off the former computer hacker's internet access for publishing an array of emails belonging to Democratic nominee Hilary Clinton's campaign in a bid to impact the vote.
In March, Swedish prosecutors offer to question Assange in London. The passport was reportedly granted to him on December 12.
Assange's newfound citizenship has again escalated tensions with Britain, though it's likely that he'll leverage the status to make a move out of the Ecuadorian embassy once and for all.
A United Nations panel concluded in 2016 that Assange was under arbitrary detention.
Assange had hinted Wednesday that something was afoot when he tweeted a picture of himself wearing an Ecuadoran soccer jersey, and Reuters reported that his name had been recorded in a civil registry of Ecuadoran citizens.