The National Security Agency has disputed Edward Snowden's insistence that he made efforts to raise his concerns about its surveillance practices internally before he decided to go public.



Releasing an email exchange it claimed to be the only record it could find of such an effort by Snowden, the agency said on Thursday he was merely “asking for an explanation of some material that was in a training course he had just completed”.



Six months ago, the agency issued a statement saying it had “not found any evidence to support Mr Snowden's contention that he brought these matters to anyone's attention”.



The email exchange with the NSA's Office of General Counsel, dated April 2013, emerged after Snowden repeated his claim to have attempted an internal whistleblowing during an interview with NBC that aired on Wednesday night.



Snowden told interviewer Brian Williams: “I actually did go through channels, and that is documented. The NSA has records, they have copies of emails right now to their Office of General Counsel, to their oversight and compliance folks, from me raising concerns about the NSA’s interpretations of its legal authorities.

“The response, more or less, in bureaucratic language, was: ‘You should stop asking questions.’”



Snowden's description appears to match parts, if not all, of the newly emerged email, which was made public on Thursday via the Senate intelligence chair, Dianne Feinstein.



“Hello, I have a question regarding the mandatory USSID 18 training,” writes Snowden to a redacted address that appears to be in the Office of General Counsel.



He goes on to cite a list provided in the training that ranks presidential executive orders alongside federal statutes in the hierarchy of orders governing NSA behaviour.



“I'm not entirely certain, but this does not seem correct, as it seems to imply Executive Orders have the same precedence as law,” adds Snowden.



“My understanding is that EOs may be superseded by federal statute, but EO's may not override statute. Am I incorrect in this?”

In a reply which was cc'd to a number of redacted email addresses, Snowden is told by an unnamed individual that he is “correct that EO's cannot override a statute” but that they have the “force and effect of law”.

The issue is an important one in the context of whether NSA surveillance activities were permissible, as it addresses possible conflict between laws passed by Congress and orders given by the White House.

Senate intelligence committee members Ron Wyden and Mark Udall have long argued the administration may have been in breach of surveillance statutes in its activities. They were prevented from raising many of their concerns in public due to confidentiality requirements.

The NSA, however, disputes that this latest email exchange is proof of Snowden raising concerns about “interpretations of its legal authorities”.



“The email did not raise allegations or concerns about wrongdoing or abuse, but posed a legal question that the Office of General Counsel addressed,” said the agency in a statement released on Thursday.



It added: “There are numerous avenues that Mr Snowden could have used to raise other concerns or whistleblower allegations.



“We have searched for additional indications of outreach from him in those areas and to date have not discovered any engagements related to his claims.”



The denial was repeated by the White House, which went further than it normally does when asked by an NBC reporter about the possibility of Snowden's return to the US and stated: “Clemency is not on the table.”



“There are avenues available to somebody like Mr Snowden to raise those kind of concerns,” added Obama spokesman Jay Carney.



Senator Feinstein said the email had been provided to her committee on 10 April, in response to a request, and added: “It does not register concerns about NSA’s intelligence activities, as was suggested by Snowden in an NBC interview this week.”



Ben Wizner, Snowden’s legal adviser, said of the email: “This whole issue is a red herring. The problem was not some unknown and isolated instance of misconduct. The problem was that an entire system of mass surveillance had been deployed – and deemed legal – without the knowledge or consent of the public. Snowden raised many complaints over many channels. The NSA is releasing a single part of a single exchange after previously claiming that no evidence existed.”



During the interview, Snowden also repeated his calls for full disclosure of the communication trail.



“I would say one of my final official acts in government was continuing one of these communications with a legal office,” he told NBC.



“And in fact, I’m so sure that these communications exist that I’ve called on Congress to write a letter to the NSA to verify that they do.”



Six months ago, responding to questions on the subject from Washington Post reporter Barton Gellman, the NSA issued a statement claiming there was no evidence of a paper trail at all.



“After extensive investigation, including interviews with his former NSA supervisors and co-workers, we have not found any evidence to support Mr Snowden's contention that he brought these matters to anyone's attention," said the agency.