WASHINGTON - The American National Security Agency (NSA) has been gathering nearly 5 billion records a day on the location of mobile phones outside the United States, enabling the agency to track the movements of individuals in what leaked documents call an effort to find suspicious travel patterns or coordinated activities by intelligence targets.

Citing the documents provided by former intelligence contractor Edward Snowden, who now lives in Moscow, The Washington Post said the phone records that are gathered include those of Americans living abroad.

The report said the NSA is able to access billions of records by tapping into worldwide mobile network cables. The NSA inadvertently gathers US location records, along with the billions of other records it collects by tapping into worldwide mobile network cables, the Post reported.

The database and projects designed to analyze it have created a mass surveillance tool for the NSA, allowing it to monitor individuals in a way never seen before.

NSA analysts can look at the data and track an individual’s movements throughout the world. They can then map out the person’s relationships with others and expose previously unknown correspondence. The agency collects the large amount of cell phone data in order to find out who is interacting with targets the agency is already tracking, even though most of the records collected are not relevant to national security.

The number of Americans who are tracked as part of the data collection overseas is unclear from the Snowden documents, and a senior intelligence official told the Post it is “awkward for us to try to provide any specific numbers.”

US officials told the Post the programmes that collect cell phone data are strictly geared towards tracking foreign intelligence targets, and are not against the law.

In October, The New York Times reported the agency carried out a secret test project in 2010 and 2011 to collect large amounts of data on the location of Americans’ cellphones inside the United States. James Clapper, the director of national intelligence, confirmed the existence of the test programme but said that it was never put into practice.

At the time, Clapper said that the United States was not collecting location information on Americans under Section 215 of the Patriot Act, which the agency says is the basis for its formerly secret programme to collect telephone logs - another term for metadata - of all domestic calls The domestic logs are collected directly from telephone companies, it was pointed out.

The overseas collection described in the latest documents do not appear to raise legal questions in the United States, even though it is likely that cellphones carried by many Americans overseas would be included in the collection effort, the report said. Still, the revelation is certain to stoke further resentment by foreigners because the scope of NSA spying overseas seems to widen with the leak of each new document.

The American Civil Liberties Union, in a statement, protested the collection of cellphone data on such a wide scale, saying that the program was particularly disturbing “given the substantial number of Americans having their movements recorded by the government.”

The premise of the NSA’s overseas tracking programme seems to be that algorithms can sift through billions of records and pick out suspicious activity like a terrorist planning session, or a series of phone calls to initiate an attack. The agency’s algorithms - like the methods used to track a contagion in a disease outbreak - would follow intelligence targets and provide agents with information on what sort of plan is afoot and how to stop it.

The NSA has been either reluctant or unable to provide detailed information on whether its vast collection programs have an extensive record of pulling those needles out of the haystack of data, the report said.

It has long been standard in criminal investigations to use cellphone tracking data as a way of finding a suspect’s location. It can be “triangulated,” for example, based on its relative proximity to nearby cell towers.