Snowden, who fled first to Hong Kong then Moscow after leaking information about the NSA's massive cellphone and Internet monitoring program, said there was "zero chance the Russians or Chinese have received" any of the documents he obtained, The New York Times reported Thursday.
Snowden said he gave all of the classified documents he had to journalists he met in Hong Kong before flying to Moscow in June and didn't keep copies for himself.
He told the Times he didn't take files to Russia "because it wouldn't serve the public interest."
In August, Russia granted Snowden temporary asylum. He was holed up in the transit zone of Moscow's Sheremetyevo International Airport since June 23 after arriving from Hong Kong.
Snowden said he could protect the documents from China's spies because he was familiar with China's intelligence abilities because he targeted China's operations and taught a course on Chinese cyber counter-intelligence as an NSA contractor.
U.S. intelligence officials have expressed concern that the files may have reached foreign intelligence services, but Snowden told the Times he believed the NSA knew he didn't cooperate with Russia or China.
Snowden, 30, has been hailed by privacy advocates and ripped by government officials as a traitor. He is facing charges under the Espionage Act for leaking the NSA information to the news media.
In the interview with the Times, Snowden said he believes he is a whistle-blower who was acting in the nation's best interests by revealing information about the NSA's surveillance program and huge collections of communications data, including that of Americans.
"The secret continuance of these programs represents a far greater danger than their disclosure," he said, adding that he was concerned that Americans had not been told about breadth of the NSA programs rather than a specific surveillance operation.
"So long as there's broad support amongst a people, it can be argued there's a level of legitimacy even to the most invasive and morally wrong program, as it was an informed and willing decision," he said. "However, programs that are implemented in secret, out of public oversight, lack that legitimacy, and that's a problem. It also represents a dangerous normalization of 'governing in the dark,' where decisions with enormous public impact occur without any public input."
The Times said Snowden was interviewed over several days last week via encrypted online communications.
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