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National Security Agency whistleblower Edward Snowden possesses enough information to cause more damage to the United States government than “anyone else has ever had in the history” of the country, according to the journalist who first reported the former contractor’s leaked documents.

Glenn Greenwald, a columnist for The Guardian newspaper who first reported on the intelligence leaks, told Argentinian newspaper La Nacion that the U.S. government should exercise extreme care with Snowden because he has the potential to do further damage to the country.

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“But that's not his goal,” Greenwald told the newspaper. “His objective is to expose software that people around the world use without knowing what they are exposing themselves to, without consciously agreeing to surrender their rights to privacy. He has a huge number of documents that would be very harmful to the U.S. government if they were made public.”

Greenwald also told The Associated Press that disclosure of the information in the documents would “allow somebody who read them to know exactly how the NSA does what it does, which would in turn allow them to evade that surveillance or replicate it.”

Greenwald said “literally thousands” of documents taken by Snowden constitute “basically the instruction manual” for how the NSA is built.

"In order to take documents with him that proved that what he was saying was true he had to take ones that included very sensitive, detailed blueprints of how the NSA does what they do," said Greenwald, adding that the interview took place about four hours after his last interaction with Snowden.

Greenwald believes the disclosure of the information in the documents would not prove harmful to Americans or their national security, but said Snowden has insisted they not be made public.

"I think it would be harmful to the U.S. government, as they perceive their own interests, if the details of those programs were revealed," said Greenwald, who has previously said the documents have been encrypted to help ensure their safekeeping.

On Friday, Snowden, 30, emerged after weeks of hiding in a Moscow airport and said he was willing to meet President Vladimir Putin’s condition that he stop leaking U.S. secrets if it means Russia would grant him asylum until he can move on to somewhere in Latin America.

Snowden is believed to be stuck in the transit area of Moscow’s main international airport, where he arrived from Hong Kong on June 23. Although he has had asylum offers from Venezuela, Nicaragua and Bolivia, the logistics of reaching whichever country is complicated since his U.S. passport has been revoked.

Despite his predicament, Snowden remains "calm and tranquil," Greenwald said.

"I haven't sensed an iota of remorse or regret or anxiety over the situation that he's in," said Greenwald. "He's of course tense and focused on his security and his short-term well-being to the best extent that he can, but he's very resigned to the fact that things might go terribly wrong and he's at peace with that."

Greenwald said he worried that interest in Snowden's personal saga had detracted from the impact of his revelations, adding that Snowden deliberately rebuffed nearly all requests for interviews to avoid media scrutiny. He also said he’s “concerned” about Snowden’s personal safety.

Greenwald said the U.S. has shown it's "willing to take even the most extreme steps if they think doing so is necessary to neutralize a national security threat.”

Asked about a so-called dead man's pact, which Greenwald has said would allow several people to access Snowden's trove of documents were anything to happen to him, Greenwald replied that "media descriptions of it have been overly simplistic.

"It's not just a matter of, if he dies, things get released, it's more nuanced than that," he said. "It's really just a way to protect himself against extremely rogue behavior on the part of the United States, by which I mean violent actions toward him, designed to end his life, and it's just a way to ensure that nobody feels incentivized to do that."

Greenwald has also co-authored a series of articles in Rio de Janeiro's O Globo newspaper focusing on NSA actions in Latin America. He said he expected to continue publishing further stories based on other Snowden documents over the next four months. Upcoming stories would likely include details on "other domestic spying programs that have yet to be revealed," but which are similar in scope to those he has been reporting on. Greenwald did not provide further details on the nature of those programs.

It remains unclear whether Russia will take Snowden up on his latest request for asylum, which could further test U.S.-Russia relations. Following Friday's meeting between Snowden and human rights activists, U.S. officials criticized Russia for allowing a "propaganda platform" for the NSA leader.

White House spokesman Jay Carney — who said the former NSA contractor is not a human rights activist or a dissident — said Russia should instead send Snowden back to the U.S. to face the felony charges that are pending against him.

"He is accused of leaking classified information, has been charged with three felony counts and should be returned to the United States," Carney said.

The Associated Press contributed to this report.