'NSA's phone, internet spy programme helped track Headley'

The leaders of the US Senate and House Intelligence committees have defended National Security Agency's phone and internet surveillance programmes, saying it has been critical in thwarting potential terrorist attacks and also to track the 2008 Mumbai attacks' convict David Headley.

Senate Intelligence Committee Chair Senator Dianne Feinstein said that the NSA phone surveillance programme revealed in reports last week is limited in scope to viewing phone records, not listening to private conversations.

Feinstein said the phone programme had helped disrupt a 2009 plot to bomb New York City's subways.

"Feinstein said the programme also helped to track the case of David Headley, a Pakistani-American who travelled to Mumbai to scope the Taj Mahal Hotel for an attack," ABC News reported.

Headley was arrested by the US security agencies in October 2009 for scouting the targets of the Mumbai terror attack for terror organisation LeT.

He has confessed to his role and has managed a deal with the US authorities under which he escaped a death penalty.

Feinstein said the shadow of the September 11 terrorist attacks still loom in her mind, and that strong intelligence from the type of surveillance conducted by the NSA is needed to prevent future attacks.

The eavesdropping and code-breaking agency is fighting back after last week's revelations by UK's Guardian newspaper about its two surveillance programs raised privacy concerns.

One program collects hundreds of millions of US phone records while the other gathers audio, video, email, photographic and Internet search usage of foreign nationals overseas.