The U.S. electronic spying chief has said massive surveillance programs newly revealed by an ex-intelligence worker had disrupted dozens of terror plots, BBC News reported.
In a U.S. Senate hearing, National Security Agency (NSA) Director Keith Alexander defended the internet and telephone data snooping programs.
Also, U.S. Secretary of State John Kerry said they showed a "delicate but vital balance" between privacy and security.
The programs were revealed in newspaper accounts last week. Meanwhile, the leaker has pledged to fight extradition to the U.S.
Edward Snowden fled his home in Hawaii for Hong Kong shortly before reports of the top secret programs were published by the Guardian and Washington Post newspapers last week. The 29-year-old former CIA and NSA contract worker has admitted giving the newspapers information about NSA programs that seize vast quantities of data on telephone calls and internet communications from U.S. internet and telephone companies.
U.S. officials have confirmed the programs exist, with President Barack Obama saying they were closely overseen by Congress and the courts.
European leaders have expressed concerns over the scale of the programs and have demanded to know whether the rights of EU citizens had been infringed.
Intelligence officials have insisted agents do not listen in on Americans' telephone conversations. And they maintain the internet communications surveillance program, reportedly code-named Prism, targeted only non-Americans located outside of the U.S.
Meanwhile, they have defended the programs as vital national security tools.
"It's dozens of terrorist events that these have helped prevent," Gen Alexander said on Wednesday, June 12 at a hearing of the US Senate intelligence committee.
Gen Alexander said intelligence officials were "trying to be transparent" about the programs and would brief the Senate intelligence committee behind closed doors before any other information became public.
But the NSA chief said some details would remain classified "because if we tell the terrorists every way that we're going to track them, they will get through and Americans will die".
He added that he would rather be criticized by people who believed he was hiding something "than jeopardize the security of this country".
