Former US NSA contractor Edward Snowden has blasted allegations that he did not file a formal complaint to the agency before he disclosed thousands of classified government documents, it has been reported.

In a preview of an interview to be published in Vanity Fair, the whistleblower told reporters that: “The NSA at this point not only knows I raised complaints, but that there is evidence that I made my concerns known to the NSA.’s lawyers, because I did some of it through e-mail.

“I directly challenge the NSA to deny that I contacted NSA oversight and compliance bodies directly via e-mail and that I specifically expressed concerns about their suspect interpretation of the law, and I welcome members of Congress to request a written answer to this question [from the NSA].”

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The May issue of the US magazine will also see Snowden respond to claims by US investigators that he is in possession of 1.7 million classified Government files. “I know exactly how many documents I have. Zero,” he said.

The 30-year-old also said he counts himself as part of what he has dubbed the “post-terror generation” fighting to defend the American constitution, and showed his admiration for WikiLeaks “[running] toward the risks everyone else runs away from.”

“No other publisher in the world is prepared to commit to protecting sources—even other journalists’ sources—the way WikiLeaks is,” he told Vanity Fair, while distancing himself from its founder Julian Assange - calling himself “pro-accountability” rather than “anti-secrecy”.

“I’ve made many statements indicating both the importance of secrecy and spying, and my support for the working-level people at the N.S.A. and other agencies. It’s the senior officials you have to watch out for,” he told the publication.

Snowden, who fled the US for China and currently lives in Russia after he revealed extensive communication surveillance by the NSA, tackled rumours that he is an anti-US spy.

He explained that he purposefully used only his personal credit card while in Hong Kong to demonstrate to the US Government that he was entirely independent and self-funded.

“My hope was that avoiding ambiguity would prevent spy accusations and create more room for reasonable debate.

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“Unfortunately, a few of the less responsible members of Congress embraced the spy charges for political reasons, as they still do to this day.

"But I don’t think it was a bad idea, because even if they won’t say it in public, intelligence-community officials are regularly confirming to journalists off the record that they know with a certainty that I am not an agent of any foreign government,” he told journalists.

The preview of the lengthy piece comes after Edward Snowden and reporter Glenn Greenwald, who brought to light the whistleblower's leaks about mass US government surveillance last year, appeared together via video link on Saturday.

The pair gave evidence to Europe's Council of Europe in Strasbourg, where Snowden accused the NSA of spying on organisations including Amnesty International and Human Rights Watch.

The council invited the White House to give evidence but it declined, according the The Guardian.