The diplomatic standoff between Britain and Ecuador deepened on Sunday after Wikileaks founder Julian Assange used an extraordinary appearance on the first-floor balcony of Ecuador's London embassy to criticise the United States.

With Metropolitan police officers watching from metres away, Assange called on President Obama to abandon what he called a "witch-hunt" against WikiLeaks.

Assange also took the opportunity to publicly thank Ecuador's President Rafael Correa for granting him political asylum.

Britain has insisted that if Assange steps outside of the Ecuador embassy, where he has sought refuge over the last 2 months, he will be detained and sent to Sweden to face sexual assault allegations.

The 41 year old Australian and his supporters claim the Swedish case is the first move of a Washington-orchestrated plot to make him stand trial in the U.S. where he fears facing prosecution and long-term imprisonment.

The White House earlier stressed that Assange's fate is an issue for Sweden, Britain and Ecuador to resolve.