"Giving asylum to Assange would be used as ammunition to attack the country," Ambassador Nathalie Cely said in a radio interview.
Since last month, Assange has been holed up in Quito's embassy in London, seeking political asylum to avoid being extradited to Sweden on rape charges.
Quito has said it is examining the request, and examining the allegations of sexual misconduct against the Australian national as part of the process.
He maintains he only had consensual sexual relations with the alleged victims.
Cely said salvos already have been launched by pressure groups seeking to "disparage her country in the eyes of US business leaders and policymakers."
In the interview with Radio Majestad, the envoy said that recriminations against Quito for sheltering Assange "already have begun."
Cely said her government remained "ready as ever to defend our position and our decisions," without providing any clues as to when Ecuador might make its decision on Assange's fate.
WikiLeaks and Assange enraged the United States by publishing a flood of secret information about the wars in Iraq and Afghanistan.
The website founder fears that if extradited to Sweden, he will be subsequently re-extradited to the United States to stand trial for espionage, on account of the 250,000 US diplomatic cables that were published.
Ecuador's leftist President Rafael Correa -- who has often been at odds with Washington and offered Assange asylum in 2010 -- has said that the South American country will take its time considering the application.
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