The National Security Agency is recording all telephone calls and their routing data in one foreign country and retaining that information for a month so that it can be analyzed later, according to a report based on a top secret intelligence document.

Similar but less comprehensive efforts exist in at least four other foreign countries, according to a classified 2013 document provided by Edward J. Snowden, the former agency contractor.

The collection effort was first disclosed on Tuesday by The Washington Post, which cited a classified summary of the program, code-named Mystic. The Post account said that the summary, also leaked by Mr. Snowden, noted that “every single” phone call in one foreign country was saved for 30 days before being purged.

With each new disclosure of N.S.A. spying programs and their deep reach into communications around the globe, the data known to be retained by the agency grows. Still, it is not surprising that spy agencies can now record every call in a country, given the declining costs of data storage, said John Villasenor, a professor at the University of California, Los Angeles, who is also affiliated with the Brookings Institution.