A senior US intelligence official says that the secret programme that tracked hundreds of millions of domestic phone records helped disrupt a 2009 terror plot to bomb New York City subways.
The official says the plot was thwarted because of the secret collection of phone records by the National Security Agency. The official would not provide other details.
The official was not authorised to discuss the plot publicly and requested anonymity.
Afghan-American Najibullah Zazi pleaded guilty to the 2009 plot, saying he had been recruited by al-Qaida in Pakistan.
Newspaper reports revealed this week that the NSA has been collecting the phone records of hundreds of millions of Americans each day for a database used to determine whether terror suspects have been in contact with people in the US.
