LONDON — Beyond the reach of police officers waiting to arrest him and with hundreds of supporters looking on, Julian Assange, the founder of WikiLeaks, took to the balcony of Ecuador’s embassy here on Sunday to condemn the United States government and cast himself as one of the world’s most persecuted whistle-blowers.

Since June, Mr. Assange has been confined to the embassy, a small office in a red-brick apartment block where he fled and was granted asylum from British efforts to extradite him to Sweden. He is wanted for questioning on accusations of rape, sexual molestation and unlawful coercion brought by two women in Stockholm in 2010, allegations he has denied.

On Sunday, with his supporters shouting encouragement, Mr. Assange did not directly mention those allegations or the women who brought them. One supporter who spoke before him, a former British diplomat, Craig Murray, asserted that Mr. Assange had been “fitted up with criminal offenses” as a pretext to prosecute him in the United States for leaking classified government documents.

It was a theme Mr. Assange continued. “I ask President Obama to do the right thing,” he said, reading from a statement as he stood on the balcony wearing a crisp blue shirt and red tie, his white hair cut short. “The United States must renounce its witch hunt against WikiLeaks. The United States must dissolve its F.B.I. investigation,” a reference to persistent reports that such an investigation is taking place. “The United States must vow that it will not seek to prosecute our staff or our supporters.”