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Whistle-blower Edward Snowden has challenged the National Security Agency to explicitly deny that he tried, before leaking secret documents to journalists, to use legal, internal means to raise a red flag about the possibly unconstitutional nature of the outfit's surveillance programs.

"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 [from the NSA] to this question," Snowden told Vanity Fair in a feature that's scheduled for publication later this week.

The challenge came in response to a claim by NSA Deputy Director Rick Ledgett, who led the agency's investigation of Snowden and who Vanity Fair says told the magazine that Snowden made no formal complaints and that no one at the NSA has reported Snowden mentioning his concerns to them.

It's a key point. Snowden -- who's currently riding out a yearlong period of temporary asylum in Russia -- is wanted by US authorities under the Espionage Act, and the president of the United States himself has said that Snowden had other avenues at his disposal and shouldn't have leaked secret files.

"The benefit of the debate he generated was not worth the damage done [to national security], because there was another way of doing it," President Obama told the New Yorker in a profile published in January.

Snowden, however, has maintained that he leaked the documents only after he'd tried to work within the system. During a live Web chat, also in January, Snowden said but that "despite this, and despite the fact that I could not legally go to the official channels that direct NSA employees have available to them, I still made tremendous efforts to report these programs to co-workers, supervisors, and anyone with the proper clearance who would listen."

Beyond that, Snowden said he anticipated from the get-go that he'd be accused of being a spy. That's why, he said, he used his personal credit card to check into the Hong Kong hotel where he stayed immediately after fleeing with the documents. As Vanity Fair puts it, he did this so the "government could immediately verify he was entirely self-financed, was independent, and had, over time, withdrawn enough financial resources to survive on his own without assistance."

"My hope was that avoiding ambiguity would prevent spy accusations and create more room for reasonable debate," Snowden told the magazine. "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."

In January, the heads of the House and Senate Intelligence Committees suggested Snowden may have been working for Russian spy agencies while employed as an NSA contractor. Snowden flat-out denied the allegation in an interview with The New Yorker, and said, "This 'Russian spy' push is absurd." And The Washington Post's Fact Checker blog said of the accusatory lawmakers that "there are...some hard questions they need to answer before they continue with the Russian spy theme."

In the Vanity Fair piece, Snowden also addressed the swirl of numbers that have been bandied about in regard to how many NSA documents he might still have in his possession. A controversial "60 Minutes" segment in December said, "There've been all kinds of figures out there about how much he took, how many documents. We've been told 1.7 million" and that Ledgett said he "wouldn't dispute" that figure. The segment went on to report that Snowden while Ledgett said it was "worth having a conversation" with Snowden about an amnesty deal provided Snowden could give assurances that "the remainder of the data could be secured."

Snowden told Vanity Fair that the 1.7 million figure is "simply a scare number based on an intentionally crude metric: everything that I ever digitally interacted with in my career."

"Look at the language officials use in sworn testimony about these records," Snowden said, "'could have,' 'may have,' 'potentially.' They're prevaricating. Every single one of those officials knows I don't have 1.7 million files, but what are they going to say? What senior official is going to go in front of Congress and say, 'We have no idea what he has, because the NSA's auditing of systems holding hundreds of millions of Americans' data is so negligent that any high-school dropout can walk out the door with it?'"

Snowden added that he has "zero" documents, echoing what he told The New York Times in October, that he gave his entire cache of classified materials to journalists before he left Hong Kong -- and kept no copies for himself. As for the journalists, Vanity Fair quotes the Guardian's US editor, Janine Gibson, as saying it's unclear how they've divvied up the trove of files: "I'm not sure we'll ever know who has what," Gibson says.

We've contacted the NSA for comment and will update this post when we hear back.