Former US National Security Agency contractor Edward Snowden leaked as many as 200,000 classified US documents to the media, according to little-noticed public remarks by the eavesdropping agency's chief late last month.

In a question-and-answer session following a speech to a foreign affairs group in Baltimore on October 31, NSA Director General Keith Alexander was asked by a member of the audience what steps US authorities were taking to stop Snowden from leaking additional information to journalists.

Former NSA contractor Edward Snowden. Credit:The Guardian

"I wish there was a way to prevent it. Snowden has shared somewhere between 50 [thousand] and 200,000 documents with reporters. These will continue to come out," Alexander said.

Alexander added that the documents were "being put out in a way that does the maximum damage to NSA and our nation", according to a transcript of his talk made available by NSA.