Assange addressed his supporters from a balcony Sunday morning in what was his first public appearance since taking refuge inside Ecuador's embassy in London two months ago.
The 41-year-old Australian addressed a crowd of more than 200 supporters, reporters and dozens of British police, as he spoke from the balcony of Ecuador's mission.
Equador granted Assange asylum on Thursday as he tries to avoid extradition to Sweden, where he is wanted for questioning in a sex crimes case. Britain insists that if he steps outside, he will be detained and sent to Sweden.
Assange and his supporters claim the Swedish case is merely the opening gambit in a Washington-orchestrated plot to make him stand trial in the U.S. over his work with WikiLeaks - something disputed by both Swedish authorities and the women involved.
"I ask President Obama to do the right thing. The United States must renounce its witch hunt against WikiLeaks," Assange said as he read aloud a written statement. "The Unites States must dissolve its FBI investigation. The United States must vow that it will not seek to prosecute our staff or our supporters."
The White House said Saturday that the Obama administration considers Assange a matter for the governments of Britain, Sweden and Ecuador to resolve.
The Associated Press contributed to this report.