WASHINGTON (Reuters) - U.S. spy agencies said on Friday that the latest media revelations based on leaks from former National Security Agency contractor Edward Snowden will likely damage U.S. and allied intelligence efforts.

On Thursday, the Guardian, the New York Times and journalistic nonprofit ProPublica published stories saying the security agency has secretly developed the ability to crack or circumvent commonplace Internet encryption used to protect everything from email to financial transactions. The stories were based on documents made public by Snowden, now a fugitive living under asylum in Russia.

The reports also said the NSA had worked with Government Communications Headquarters, its British partner, and had used a variety of means, ranging from the insertion of "back doors" in popular tech products and services, to supercomputers, secret court orders and the manipulation of international processes for setting encryption standards.

In a statement on Friday, the Office of the U.S. Director of National Intelligence, which said it was speaking on behalf of all U.S. spy agencies, did not confirm details of the media reports.

The statement did acknowledge that the U.S. intelligence community "would not be doing its job" if it did not try to counter the use of encryption by such adversaries as "terrorists, cybercriminals, human traffickers and others."

The statement said, however, that the stories published on Thursday revealed "specific and classified details about how we conduct this critical activity." It claimed that anything that the news stories added to public debate about government surveillance was "outweighed by the road map they gave to our adversaries" about specific eavesdropping methods.

(Reporting by Mark Hosenball; Editing by Karey Van Hall and Jackie Frank)