WikiLeaks founder Julian Assange has called on the US Government to "stop the witch hunt" against him, WikiLeaks and its supporters - and he claimed British police had attempted to enter the embassy on Wednesday evening.
His voice shaking, Assange said: "On Wednesday night, after a threat was sent to this embassy, and police descended on this building, you came out to watch over us. You brought the world's eyes with you.
"Inside this embassy after dark, I could hear teams of police, swarming up into the building through its internal fire escape.
"But I knew there would be witnesses. If the UK did not throw away the Vienna conventions the other night it is because the world was watching."
A huge roar from supporters greeted Assange, who appeared with his blonde hair short and dressed in a light blue shirt and red tie.
He thanked supporters for "coming out in the middle of the night" this week, many of whom camped out overnight.
He paid tribute to the "courage and loyalty, which has seen no equal" to the staff of WikiLeaks and apologised for his absence to his children.
Assange was granted asylum by Ecuador this week, but is unable to leave the embassy at risk of arrest. Ecuador has previously said that asylum would be rescinded if Assange made "political statements".
The statement marks two months that the Australian has sought refuge in the building, and is his first public comment in that time.
He is wanted in Sweden to answer sex crime allegations, but fears Sweden may extradite him to the US - in connection with his activities with WikiLeaks. The US is not currently requesting his extradition.
He said: "As WikiLeaks stands under threat, so does freedom of expression, and the health of our society.
"We must use this moment to articulate the choice which is before the government of the United States of America, to return to and reaffirm the revolutionary values it was founded upon.
"I ask President Obama to do the right thing. The United States must renounce its witch hunt against WikLeaks, dissolve its FBI investigation and vow it will not seek to prosecute our staff or our supporters."
He called for the release of whisteblowers including Bradley Manning (picture above, top right), arrested and still imprisoned two years later for allegedly passing on information to WikiLeaks.
"He must be released," Assange said, "he is a hero and an example to all of us and one of the world's foremost political prisoners."
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The UK Foreign Office told The Huffington Post UK it would be make no comment on Sunday's speech, and that Foreign Secretary William Hague's speech this week, that Assange would not be allowed to leave the country, still stood.
Rumours abounded before the statement, with supporters speculating that Assange would film his statement, or speak from the porch - to avoid potential arrest if he stepped outside.
Workmen removed a doorframe from the first floor balcony - still low enough for a tall policeman to have been able to grab Assange's ankle - to allow the campaigner to speak to demonstrators.
Former British ambassador Craig Murray and journalist Tariq Ali spoke to the crowd before the statement, in support of Assange.
Despite hints from the British government that police could legally enter the embassy and arrest Assange, it would be an unlikely move.
Earlier this morning, Assange's legal advisor Baltasar Garzon addressed journalists and crowds outside the embassy in Knightsbridge, telling them he had been instructed to carry out "legal action".
He said: "I have spoken to Julian Assange and I can tell you he is in fighting spirits and he is thankful to the people of Ecuador and especially to the president for granting asylum.
"Julian Assange has always fought for truth and justice and has defended human rights and continues to do so.
"He demands that WikiLeaks and his own rights be respected.
"Julian Assange has instructed his lawyers to carry out a legal action in order to protect the rights of WikiLeaks, Julian himself and all those currently being investigated."
On Friday evening Ecuadorian president Rafael Correa delivered a harsh warning to Britain against the suggestion that police may storm the embassy, claiming that would destroy ties between the two countries and that Britain "did not know who they were dealing with."
He said: "The United Kingdom threat would be breaking the law and encroaching on our embassy. I don’t know who they think I am or what they think our government is. But how could they expect us to yield to their threats or cower before them?
"My friends, they don’t know who they are dealing with."
The bad feeling between the UK and Ecuador could spread to other South American nations. The Organisation of American States, which includes all 35 nations in North and South America, will meet next Friday to discuss Assange's asylum.
The US, Canada and Trinidad and Tobago all opposed the resolution to discuss the meeting, but 23 members voted in favour.
The OAS secretary general, José Miguel Insulza, said the discussion would be on "the problem posed by the threat or warning made to Ecuador by the possibility of an intervention into its embassy in London.
"The issue that concerns us is the inviolability of diplomatic missions of all members of this organisation, something that is of interest to all of us."