The distinction means the extraordinary surveillance programme is not overseen by a secretive US intelligence court but is regulated by some US lawmakers, Obama administration insiders and inspectors general.
Documents obtained from former NSA contractor Edward Snowden showed that the NSA gathers as many as 5 billion records every day about the location data for hundreds of millions of cellphones worldwide by tapping into cables that carry international cellphone traffic.
The Washington Post said the collection inadvertently scoops up an unknown amount of US data as well.
The NSA has declined to provide any estimates about the number of Americans whose cellphones it has tracked because they were travelling overseas or their data was irrevocably included in information about foreigners' cellphones.
"It is not ubiquitous," NSA spokeswoman Vanee Vines said in a statement. "NSA does not know and cannot track the location of every cell phone."
Vines said the collection of the global cellphone location data is carried out under the White House order that governs all US espionage, known as Executive Order 12333.
A frequent justification for the NSA programmes by President Barack Obama and top US intelligence officials is that they are overseen by all three branches of government.
"The NSA claims its collection is incidental, but there is no question it's deliberately engaging in the mass collection of cell phone location data that it knows will inevitably sweep up information on a huge number of innocent Americans," said Catherine Crump, American Civil Liberties Union staff attorney, in a statement. "And, all of this is happening without any supervision by a court."
But an intelligence lawyer told the Post that when US cellphone data are collected, the data are not covered by the Fourth Amendment, which protects Americans against unreasonable searches and seizures.
