Famed whistleblower and former CIA employee Edward Snowden has revealed a new batch of documents detailing how major network carrier AT&T closely collaborated with the National Security Agency to spy on Internet users.

The documents, which were obtained by the New York Times, revealed that from 2003 to 2013, AT&T has provided the NSA the means to spy on U.S. Internet traffic. This includes billions of email messages sent by citizens using local networks.

According to the files, the spying was carried out through AT&T's 17 facilities in different parts of the country. But aside from surveillance purposes, these centers were also used by the NSA to field test new spying technologies and methods.

As noted by the IT Pro Portal, the two organizations had a solid partnership since the NSA repeatedly praised AT&T for its commitment to the clandestine operation. The government agency even reminded its agents to be courteous to AT&T staff members especially when visiting the company's facilities.

"This is a partnership, not a contractual relationship," the NSA stated in the documents.

Aside from spying on ordinary users, AT&T also assisted the NSA in monitoring the online communications of the United Nations, which is a client of the network carrier.

According to Reuters, the NSA was able to do so through a secret court order carried out by the company. This gave the government agency permission to wiretap the international organization.

Also, as part of its partnership with AT&T, the NSA was given access to the data collected by other telecoms and Internet service providers operating in the U.S.

When asked regarding its partnership with the NSA and the other details revealed by Snowden's documents, AT&T noted that it only works with authorities if the situation calls for it.

"We do not voluntarily provide information to any investigating authorities other than if a person's life is in danger and the time is of the essence," spokesperson Brad Burns told Reuters. "For example, in a kidnapping situation we could provide help tracking down called numbers to assist law enforcement."