Washington, May 5 (RHC)-- The U.S. National Security Agency (NSA) collected over 530 million records of phone calls in 2017, more than triple gathered a year before, an intelligence agency report shows. 

The call detail records, which were collected under Foreign Intelligence Surveillance Act (FISA), include the numbers and the time and duration of the phone calls, but not their content, showed the report released by the Office of the Director of National Intelligence on Friday. 

According to a spokesman for the office, the NSA had discovered that some factors can affect the number of call records collected and that the agency expects them to "fluctuate from year to year." 

"The government has not altered the manner in which it uses its authority to obtain Call Detail Records pursuant to the FISA. Rather, the NSA has found that a number of factors may influence the number of Call Detail Records that NSA receives," said Tim Barrett. 

"These factors include the number of Court-approved selection terms -- like a phone number -- that are used by the target; the way targets use those selection terms; the amount of historical data that providers retain; and the dynamics of the ever-changing telecommunications sector," he added. 

The dramatic increase happened during the second full year of a new surveillance system established at the spy agency following a law passed by US lawmakers in 2015 that aimed to restrict and boost oversight of the spy agency's surveillance program. 

Robyn Greene, policy counsel at the Washington-based Open Technology Institute that focuses on digital issues, said, "The intelligence community's transparency has yet to extend to explaining dramatic increases in their collection." 

Friday's report also indicated an increase in the number of foreigners living outside the U.S. who were targeted under a warrant-less internet surveillance program, known as Section 702 of the Foreign Intelligence Surveillance Act, which Congress renewed earlier this year. 

That figure went up from 106,469 in 2016 to 129,080 in 2017, the report said, adding it is up from 89,138 targets in 2013, or a cumulative rise over five years of about 45 percent. 

In 2013, former NSA contractor Edward Snowden leaked details of the agency's global surveillance programs, including its collection of data on Americans. 

The disclosure of such details dealt a heavy blow to the U.S. government, causing it an international scandal.