Leaks revealing how American spies have circumvented encryption for online communications are "not news" because code-breaking is part of their job, US intelligence said on Friday.
But revelations to newspapers about how the National Security Agency (NSA), along with British spy services, have deciphered data under encryption could help America's adversaries, the office of the director of national intelligence said in a statement.
"While the specifics of how our intelligence agencies carry out this cryptanalytic mission have been kept secret, the fact that NSA's mission includes deciphering enciphered communications is not a secret, and is not news," the ODNI said in a statement.
"It should hardly be surprising that our intelligence agencies seek ways to counteract our adversaries' use of encryption," the ODNI said.
"Throughout history, nations have used encryption to protect their secrets, and today terrorists, cybercriminals, human traffickers and others also use code to hide their activities," it said.
"Our intelligence community would not be doing its job if we did not try to counter that," the office said.
The ODNI noted that the National Security Agency's website describes its mission to include "cryptology."
The statement came a day after the latest dramatic disclosures about the scale of American electronic surveillance, based on leaks from former US intelligence contractor Edward Snowden.
Documents handed over by Snowden to The Guardian, The New York Times and ProPublica suggest US and British intelligence agencies are able to penetrate supposedly secure encryption used to protect emails, banking transactions and phone conversations.
The National Security Agency, working with its British counterpart, GCHQ, accomplished the feat by using supercomputers, court orders, and some cooperation from technology firms, according to the leaked documents.
The ODNI expressed concern that the details divulged by Snowden could undermine efforts to track threats posed to the United States and its allies.
"The stories published yesterday, however, reveal specific and classified details about how we conduct this critical intelligence activity."
"Anything that yesterday's disclosures add to the ongoing public debate is outweighed by the road map they give to our adversaries about the specific techniques we are using to try to intercept their communications in our attempts to keep America and our allies safe ...," the ODNI statement said.
The reports noted that US intelligence officials asked the news organizations not to publish articles on the subject, fearing it would prompt foreign targets to switch to new forms of encryption or communications that would be harder to collect or read.
ProPublica, an independent, non-profit organisation devoted to investigative journalism which has partnered with The Guardian and The New York Times to review documents from Snowden, said it decided to go ahead with the report because of its importance to the public.