Former National Security Agency systems analyst Edward Snowden says he did not take any secret NSA documents to Russia and that intelligence officials in China as well as Russia could not get access to the documents he had obtained before leaving the United States.

In an interview with The New York Times, Snowden said he handed over all the documents he had obtained to journalists during his stay in Hong Kong. The newspaper posted its story on its website Thursday.

Snowden said he did not retain copies of the documents and did not take them to Russia "because it wouldn't serve the public interest", the Times reported.

"There's a zero percent chance the Russians or Chinese have received any documents," he said.

Snowden's leaks of highly classified material have resulted in numerous news stories about US surveillance activities at home and abroad and sparked debate about the legality of those activities and the privacy implications for average US citizens.

The Times reported that in the interview, which it said took place over several days in the last week and involved encrypted online communications, Snowden asserted that he believed he was a whistle-blower who was acting in the nation's best interests by revealing information about the NSA's surveillance dragnet and huge collections of communications data.

Snowden said he had helped US national security by prompting a badly needed public debate about the scope of the intelligence effort. "The secret continuance of these programs represents a far greater danger than their disclosure," he said.

Snowden faces espionage charges in the US. On Aug 1 he was granted asylum in Russia, which is allowing him to remain there for one year.