A two-minute mashup including remarks NSA Director Keith Alexander made Wednesday about surveillance programs and information leaks. (AFCEA)

Gen. Keith B. Alexander, the director of the National Security Agency, provided new details Thursday about the extent to which the government believes its sweeping surveillance powers have led to the disruption of terrorist plots or the arrest of suspects.

Speaking at conference in Baltimore, Alexander said that because of the surveillance programs, 42 terrorist plots were disrupted and 12 individuals were identified as having provided material support to terrorist groups. Of the 54 cases he referred to, Alexander said only 13 had a “homeland nexus” and the rest involved cases overseas. Alexander said 25 occurred in Europe, 11 in Asia and five in Africa.

Alexander said both the NSA’s ability to collect the communications of foreign targets overseas using U.S. Internet firms and the collection of Americans’ phone records had contributed separately to counterterrorism efforts.

“With these exceptional authorities came equally exceptional oversight by all three branches of the government,” said Alexander.

In the case of the collection of metadata on the phone use of Americans, Alexander said it is kept in “a virtual lockbox” which the NSA can access only if “we have reasonable, articulable suspicion.”

The United States has described a small number of domestic cases in which NSA powers authorized by the USA Patriot Act and its amendments have led to arrests, including a plan to conduct suicide bombings in the New York subway system. But there has been no information on any foreign plot, and the details of those cases remain classified.

German Chancellor Angela Merkel said that “tips from American sources” had foiled a 2007 plot to attack U.S. troops and citizens in Germany. Four Islamist extremists were convicted of terrorism charges, including planning a massive car bombing near a U.S. Air Force base in Germany.

“Our allies have benefited,” Alexander said Thursday. He bemoaned leaks about the programs by a former NSA contractor, Edward Snowden, who turned over highly classified NSA documents to The Washington Post and the British newspaper the Guardian.

“What is going on in these leaks is unconscionable in my opinion,” he said. “It hurts our nation and our allies, and it’s flat wrong.”

Two Democratic senators, Ron Wyden of Oregon and Mark Udall of Colorado, have questioned whether the collection of tens of millions of domestic calling records has helped thwart plots.

“It appears that the bulk phone records collection program under section 215 of the USA Patriot Act played little or no role in most of these disruptions,” the senators said in a statement. They did note that targeting foreign communications under Section 702 of the Foreign Intelligence Surveillance Act was useful but that conflating these programs as one effort was misleading.