The National Security Agency is able to collect a nation’s “every single” phone call and store the voice recordings for a month, according to a new Edward Snowden leak that reveals further details on the NSA’s bulk data collection practices for intelligence operations. The Washington Post has learned that the NSA’s MYSTIC voice interception program began in 2009, with the agency developing a RETRO tool that can access any voice calls from the targeted nation for a period of 30 days.

The first nation was targeted with the MYSTIC/RETRO combo in 2011, and as many as six more countries may be spied upon using the voice call recording tools in the future. The publication was asked by U.S. officials not to reveal what country MYSTIC has been used on.

Apparently, the program was successful enough bringing in “high-stakes intelligence that would not have existed under traditional surveillance programs in which subjects were identified for targeting in advance,” according to the Post. “Unlike most of the government’s public claims about the value of controversial programs, [highly classified] briefings supply names, dates, locations and fragments of intercepted calls in convincing detail.”

With the help of the program, the NSA can tap in a nation’s call network, intercept calls and listen to any of the voice conversations of a specific number that has been associated with a target for a period of 30-days, allowing the agency to basically “open a door ‘into the past’” for relevant information. The NSA can further store pertinent data related to a target, while old recordings are simply deleted after 30 days and replaced with new ones. A previous report revealed that the NSA collects a huge amount of handset location data each day using information taken from the carriers’ towers to determine locations for certain targets and eventual associations between people.

In fact, one of the problems with MYSTIC is the huge amount of data that needs to be stored. In the first year of use, a program officer wrote that the project “has long reached the point where it was collecting and sending home far more than the bandwidth could handle.”

Thus, the NSA is further expanding its cloud-based collection systems, with a “gargantuan new ‘mission data repository’” being built in Utah. Christopher Soghoian,the American Civil Liberties Union’s principal technologist said that history suggests that “over the next couple of years they will expand to more countries, retain data longer and expand the secondary uses.”

Voice calls from American citizens in the targeted countries are also captured by the MYSTIC system, as the NSA apparently doesn’t attempt to filter them out. These calls are “acquired incidentally as a result of a collection directed against appropriate foreign intelligence targets.” Meanwhile, the NSA said that its intelligence gathering activities operate within the law.