The US government released an email on Thursday written by Edward Snowden, in a bid to debunk his claim that he raised concerns about mass spying programs before fleeing and engineering huge media leaks.
Snowden, now exiled in Russia, said in an interview aired by NBC on Wednesday that he had gone through official channels to question the legality of National Security Agency surveillance.
No emails from Snowden on abuse: White House
The former intelligence contractor mentioned a specific email he had written to the NSA General Counsel's Office detailing his concerns.
In response, the agency released what President Barack Obama's administration said was the only such communication found in the archives from Snowden on the issue, and said it did not prove his claims.
But Snowden subsequently told The Washington Post that the NSA's release was "incomplete," pointing to additional correspondence with the agency's Signals Intelligence Directorate.
Snowden said he had also raised concerns about the NSA's use of data from major US Internet companies.
In the April 2013 email, Snowden asked NSA lawyers to clarify a question about the relative authority of executive orders released by the president and legal statutes.
The exchange does not in itself appear to register a complaint or concern about the mass phone data surveillance programs that he later exposed in a series of leaks to media organizations.
Read: 'No relationship' with Russian govt, says Snowden
"The email did not raise allegations or concerns about wrongdoing or abuse but posed a legal question that the Office of General Counsel addressed," White House spokesman Jay Carney said.
"There was not additional follow-up noted."
In December, the NSA claimed it had never received any such communication from Snowden.
"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," NSA spokeswoman Vanee Vines said at the time.
Responding to the latest email release, Snowden expressed confidence that the "truth" would soon become clear.
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"If the White House is interested in the whole truth, rather than the NSA's clearly tailored and incomplete leak today for a political advantage, it will require the NSA to ask my former colleagues, management and the senior leadership team about whether I, at any time, raised concerns about the NSA's improper and at times unconstitutional surveillance activities," Snowden told the Post.
"It will not take long to receive an answer."
Plenty of avenues for complaints
The White House maintains there were plenty of avenues Snowden could have taken to raise concerns about the legality and scope of NSA programs instead of leaking huge amounts of classified material to journalists.
"The appropriate authorities have searched for additional indications of outreach from Mr Snowden in those areas and to date have not found any engagements related to his claims," Carney said.
But Snowden maintained in the NBC interview that he did go through official channels.
"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," he said.
"The response more or less, in bureaucratic language, was, 'You should stop asking questions.'"
Snowden also told NBC he was open to the possibility of clemency or amnesty and would like to return home one day.
But the former intelligence contractor maintained he had carried out a patriotic act by exposing huge surveillance dragnets he said infringed the US Constitution.
The Obama administration, however, says Snowden is welcome to return home but only to face trial for exposing sensitive top secret information it says aided US enemies.