America's sweeping surveillance programmes have foiled 50 terrorist plots worldwide, including one directed at the New York Stock Exchange, according to the director of the National Security Agency.
General Keith Alexander said the two recently disclosed operations - one that gatherscUS phone records and another that is designed to track the use of US-based internet servers by foreigners with possible links to terrorism - are critical in the terrorism fight.
Intelligence officials last week disclosed some details on two thwarted attacks - one targeting the New York subway system, one to bomb a Danish newspaper office that had published the cartoon depictions of the Prophet Mohammed. General Alexander and Sean Joyce, deputy director of the FBI, offered additional details on two other foiled plots, including one targeting Wall Street.
Mr Alexander told the House Intelligence Committee the NSA was able to identify an extremist in Yemen who was in touch with an individual in Kansas City, Missouri. They were able to identify co-conspirators and thwart a plot to bomb the New York Stock Exchange.
He also said a terrorist financier inside the US was identified and arrested in October 2007, thanks to a phone record provided by the NSA. The individual was making phone calls to a known designated terrorist group overseas.
The programs "assist the intelligence community to connect the dots," General Alexander told the committee in a rare, open congressional hearing. He said the intelligence community would provide the committees with more specific on the 50 cases as well as the exact numbers on foiled plots in Europe.
Deputy NSA Director Chris Inglis said a limited number of officials at the agency could authorise dissemination of information to the FBI related to a US citizen, and only after determining it was necessary to understand a counter-terrorism issue. Information related to an American who is found not to be relevant to a counter-terrorism investigation must be destroyed, he added.
The hearing came the morning after president Barack Obama vigorously defended the surveillance programs in a lengthy interview, calling them transparent - even though they are authorised in secret.