National Security Agency Director Gen. Keith Alexander, second from right, testifies on Capitol Hill Tuesday. (J. Scott Applewhite/AP)

Intelligence officials said Tuesday that the government's sweeping surveillance efforts have helped thwart "potential terrorist events" more than 50 times since the Sept. 11, 2001 attacks, and the officials detailed two new examples to illustrate the utility of the programs.

In testimony before the House Intelligence Committee on Tuesday, officials cited a nascent plot to blow up the New York Stock Exchange and a case involving an individual providing financial support to an overseas terrorist group.

"In recent years, these programs, together with other intelligence, have protected the U.S. and our allies from terrorist threats across the globe to include helping prevent the terrorist -- the potential terrorist events over 50 times since 9/11," National Security Agency Director Gen. Keith Alexander told the committee.

He said at least 10 of the plots targeted the United States.