US Senators grill NSA chief over mass surveillance revelations

The chief of the US National Security Agency has strongly defended before lawmakers the domestic intelligence body's secret phone and internet surveillance programme, the leaked news of which has made headlines all week.

General Keith Alexander, director of the NSA, insisted before the powerful Senate appropriations committee on Wednesday that the surveillance had helped thwart dozens of terror attacks.

The hearing was not intended to focus on the recent revelations about domestic surveillance, but senators of both parties used General Keith Alexander's first public appearance on Capitol Hill since the story broke to press him for answers about how its widespread surveillance programmes operate in a tense two-hour session.

Facing sceptical questions from the lawmakers after a rogue technician revealed the secret operation to the UK newspaper The Guardian, Gen Alexander insisted it operates under proper legislative and judicial oversight.

"It's classified but it's dozens of terrorist events that these have helped prevent," he told the hearing, the first time he had been questioned in public since 29-year-old former contractor Edward Snowden spilled the beans.

Snowden was last spotted at a Hong Kong hotel on Tuesday; he has gone underground since then.

"I want the American people to know that we're being transparent in here," the NSA chief insisted, warning that "the trust of the American people" was a "sacred requirement" if his agency was to be able to do its job.

In one testy exchange, Senator Jeff Merkley, a Democrat and a Verizon customer, waved his smartphone at Alexander. "What authorised investigation gave you the grounds for acquiring my cellphone data?" Merkley asked.

Committee chairman Senator Barbara Mikulski, also a Democrat, said, "Many of us are concerned about what is the access to people and businesses' information. There are those, because of the Snowden revelation, who wonder about the government's access to that information."

Alexander said he struggled with how much detail to provide in public about the surveillance. "I would rather take a public beating, and let people think I'm hiding something, than jeopardize the security of this country," Alexander testified.

He said he would aim to declassify specific cases in which the two surveillance programs described by The Guardian had contributed to government efforts at thwarting terrorist attacks.

But Alexander added some new details about how the NSA surveillance works – and he also raised unanswered questions about it.

The two programs in question are distinct, at least as matters of law. One, justified under Section 215 of the Patriot Act, collects the phone records of millions of Americans, but is said not to examine their content. The other, justified under Section 702 of the 2008 FISA Amendments Act and known as Prism, relates to the online communications of people believed not to be inside the United States.

But Alexander said it was difficult, in practice, to separate them, and credit one of the programmes for contributing to an investigation without crediting the other. "The reality is, they work together," Alexander said.

Alexander defended the bulk collection by saying it was necessary to give the NSA the widest possible data pool so it can then query the phone-records database for specific terrorist interaction with Americans. Once the NSA has "reasonable, articulable suspicions" of a person's suspected involvement in terrorism, Alexander said, "we can go backwards in time and see who he was talking to," and pass that information to the FBI.

Alexander added that there were strict rules preventing the NSA from querying its phone records database without that suspicion, but he left it unclear who performs the certification.

Asked if the light shone on the programmes could help terrorists avoid surveillance, Alexander said, "They will get through, and Americans will die."

"Great harm has already been done by opening this up. The consequence I believe is our security has been jeopardized," he warned.