The National Security Agency is using internet data processing centers run by telecommunications powerhouse AT&T to spy on American and foreign citizens, a new investigation claims.

The Intercept has identified eight AT&T facilities across the United States which are allegedly being used by the NSA to monitor internet users' emails, social media posts and internet browsing.

The centers are known as 'peering' facilities' and processes data from both AT&T customers and those of other U.S. internet providers, as well as telecoms companies fromSweden, India, Germany and Italy.

Spy HQs: This map shows the eight locations of the AT&T facilities allegedly being used by the NSA to spy on internet users

I spy: These AT&T data processing hubs in New York City, left, and Chicago, right, are two of eight facilities allegedly being used by the NSA

'It's eye-opening and ominous the extent to which this is happening right here on American soil,' said Elizabeth Goitein, co-director of the Liberty and National Security Program at the Brennan Center for Justice told The Intercept.

'It puts a face on surveillance that we could never think of before in terms of actual buildings and actual facilities in our own cities, in our own backyards.'

All eight buildings, in cities such as Los Angeles, NYC, Seattle and Washington DC, have several things in common, as well as being AT&T facilities.

They are tall and imposing structures with few or blacked out windows, and - either seemingly or confirmed to be - built to withstand a nuclear attack.

The buildings are located on 10 South Canal Street in Chicago, 1122 3rd Avenue in Seattle, 811 10th Avenue in New York City, 30 E Street Southwest in Washington DC, 51 Peachtree Center Avenue in Atlanta, 611 Folsom Street in San Francisco, 4211 Bryan Street in Dallas and 420 South Grand Avenue in Los Angeles.

Hiding in plain sight: The processing centers, like this in San Francisco, processes data from both AT&T, other U.S. internet providers, and international telecoms companies

Listening posts: By gaining access to the data which goes through these AT&T facilities identified by The Intercept, the NSA can monitor huge amounts of internet data

Same same, but different: The AT&T buildings, such as this one in Washington DC, are all tall and imposing structures with few or blacked out windows

By tapping into wires in these 'peering' facilities, the NSA can collect 'not only AT&T's data, they get all the data that's interchanged between AT&T's network and other companies,' according to Mark Klein, a former AT&T technician who worked with the company for 22 years, told The Intercept.

'The peering links, by the nature of the connections, are liable to carry everybody's traffic at one point or another during the day, or the week, or the year,' he added.

The Intercept interviewed several former AT&T employees who confirmed the locations of the eight 'peering sites' used by the NSA.

Investigation: The report by The Intercept has been confirmed by former AT&T employees. Pictured is the AT&T facility in Dallas linked to the NSA by the website

Breaking news: The information that these hubs, like this one in Seattle, is being utilized by the NSA has been compared to spying on Americans 'in their own backyard'

The NSA would neither confirm nor deny the claims, while AT&T told The Intercept that they were required by law to provide the authorities with information to certain extents.

The telecoms giant's close relationship with the NSA was first revealed by the New York Times in 2015, thanks to documents leaked by whistle-blower Edward Snowden.

The company helped the spy agency in a broad range of classified activities, the documents revealed.

They describe how the NSA's working relationship with AT&T had enabled the agency to conduct surveillance, under various legal rules, of international and foreign-to-foreign internet communications that passed through network hubs in the United States.