Snowden’s comments come as National Security Agency Director Keith Alexander testified before Congress for the first time since Snowden’s leaks were published last week. Alexander said the NSA’s mass-collection of phone records has helped thwart dozens of attacks.

Gen. Keith Alexander: “I gave an approximate number to them in a classified — in a classified [briefing], but it’s dozens of terrorist events that these have helped prevent.”

Sen. Patrick Leahy: “Dozens?”

Gen. Keith Alexander: “For both here and abroad, in disrupting or contributing to the disruption of terrorist attacks.”

Sen. Patrick Leahy: “Out of those millions, dozens have been critical?”

Gen. Keith Alexander: “That’s correct.”

Claims that NSA spying has thwarted attacks have been the subject of debate. In a statement on the collection of phone records under the PATRIOT Act, Democratic Senators Mark Udall of Colorado and Ron Wyden of Oregon, both members of the Senate Intelligence Committee, said: “After years of review, we believe statements that this very broad Patriot Act collection has been a critical tool in protecting the nation do not appear to hold up under close scrutiny.”