Picture of NSA whistleblower Edward Snowden
Picture of NSA whistleblower Edward SnowdenReuters

U.S. surveillance efforts foiled over 50 potential terrorist events since the 2001 attacks, the head of the National Security Agency told lawmakers Tuesday in defending the programs as vital to national security, AFP reports.

"These programs are immensely valuable for protecting our nation and securing the security of our allies," said General Keith Alexander, in the latest bid by the government to deflect criticism of the telephone and Internet snooping programs that came to light last week.

"In recent years the information gathered from these programs provided the U.S. government with critical leads to help prevent over 50 potential terrorist events in more than 20 countries around the world,” he added, according to AFP.

Alexander said that "at least 10 of these events included homeland-based threats."

The NSA chief told the House Intelligence Committee that he would be providing lawmakers with information on the incidents foiled since the September 11, 2001 attacks.

"It's over 50 cases," he said, adding that the exact number was still being reviewed.

Alexander said that details of four incidents were being made public, including plots to bomb the New York Stock Exchange and the subway system in New York.

Alexander also said the programs had a sound legal foundation with oversight by courts and Congress.

"I believe we have achieved the security and relative safety in a way that does not compromise the privacy and civil liberties of our citizens," he said, according to AFP.

Alexander and other officials appeared at the hearing to discuss the firestorm after the release of news reports disclosing the vast data gathering of data of phone records and monitoring of Internet communications.

The reports said the so-called PRISM program directly obtained data from major U.S. Internet firms including Google, Yahoo! and Facebook.

But Alexander said that under this program, "the U.S. government does not unilaterally obtain information from the servers of U.S. companies.

"Rather, the U.S. companies are compelled to provide these records by US law, using methods that are in strict compliance with that law," he said.

Last week it was revealed that the man who leaked the information about the PRISM program was Edward Snowden, a 29-year-old former undercover CIA employee.

Snowden, who has contracted for the NSA and works for the consulting firm Booz Allen Hamilton, denounced what he described as systematic surveillance of innocent citizens and said in an interview that “it’s important to send a message to government that people will not be intimidated.”

He is currently hiding in Hong Kong, and his father has pleaded with his son to stop leaking information and to return home to the United States