Speaking to the Washington Post from a secret location in the country where he has been granted temporary asylum, Snowden, 30, again insisted that he acted in the interest of Americans by leaking details about surveillance by the National Security Agency eight months ago.

The contents of the files released by him into the public domain revealed the scope and depth of spying by the state on its own citizens and foreign citizens.

Russian president Vladimir Putin even quipped he "envied" his US counterpart Barack Obama for the enormous spy network deployed against America's own citizens by Washington DC.

While considered a hero by many, others accuse Snowden of compromising the US government's ability to collect intelligence on potential threats to national security, with one military expert claiming Al Qaeda have modified their means of communications in the light of the leak.

Snowden insisted he was not trying to undermine his home country on behalf of a foreign power. "There is no evidence at all for the claim that I have loyalties to Russia or China or any country other than the United States. I have no relationship with the Russian government. I have not entered into any agreements with them," he said.

"If I defected at all, I defected from the government to the public."

And in a barb which will infuriate those inside America who consider Snowden a traitor - not a hero, he claimed what he did was for the NSA's own good, saying: "I am still working for the NSA right now. They are the only ones who don't realise it."

He continued "For me, in terms of personal satisfaction, the mission's already accomplished.

"I already won. As soon as the journalists were able to work, everything that I had been trying to do was validated. Because, remember, I didn't want to change society. I wanted to give society a chance to determine if it should change itself.

"All I wanted was for the public to be able to have a say in how they are governed."

"I am not trying to bring down the NSA, I am working to improve the NSA. I am still working for the NSA right now. They are the only ones who don't realise it."

Snowden said his colleagues shared concerns about the quantity of data on American civilians gathered by the NSA, with no obvious good cause. But he said he did not oppose the principle of spying by governments.

"I don't care whether you're the pope or Osama bin Laden," he said. "As long as there's an individualised, articulable, probable cause for targeting these people as legitimate foreign intelligence, that's fine.

"I don't think it's imposing a ridiculous burden by asking for probable cause. Because, you have to understand, when you have access to the tools the NSA does, probable cause falls out of trees."