Since 2010, the NSA has been exploiting its huge collections of data to create sophisticated graphs of some Americans' social connections that can identify their associates, their locations at certain times, their travelling companions and other personal information, The New York Times reported.
The paper, quoting documents provided to it by former NSA contractor Edward Snowden, said the NSA can augment the communications data with material from public, commercial and other sources, including bank codes, insurance information, Facebook profiles, passenger manifests, voter registration rolls and GPS location information, as well as property records and unspecified tax data.
"We assume as Americans that if somebody in the government is looking at your information, it's because they have a reason, because you're suspected of a crime," Karen Greenberg, director of the Center on National Security at Fordham Law School, was quoted as saying by CNN.
The documents do not specify how many Americans' social connections have been analysed, or whether any have been implicated in wrongdoing, the report said.
More From This Section
The policy change was intended to help the NSA "discover and track" connections from a foreign intelligence subject to an American citizen, according to the leaked documents.
Defending the practice President Barack Obama has ordered a review of NSA's data collection practices because of Snowden's leaks. But the president has defended the use of such methods to gather intelligence on terrorists and other threats.
In response to the latest disclosure, the NSA again emphasised it does not listen to phone calls or read emails of Americans without obtaining a court order.