By NewsGram Staff Writer

Edward Snowden, the American whistleblower who blew the lid on global surveillance programs run by the National Security Agency (NSA) has said that such vigilance programmes can never prevent terrorism fully.

Speaking at the International Journalism Festival in Perugia on Friday, Snowden said, "Even the most extensive monitoring system would never be able to make us perfectly safe from terrorism."

"Yet, mass surveillance is often used by intelligence agencies to spy on citizens regardless if a crime is being committed or not," he added.

Snowden was welcomed as a chief guest by the audience attending the third day of the festival in a debate via video link broadcasted by the Ansa news agency. The festival has gathered journalists and experts from all over the world since 2006.

Snowden long served the National Security Agency (NSA), the Central Intelligence Service (CIA) and other American security agencies as technology and cyber-security expert.

In 2013, Snowden made a host of revelatory disclosures regarding a "global surveillance apparatus" run by the United States in cooperation with Australia, Canada and the United KIngdom, due to which he had to seek asylum away from the United States.

He is currently residing in an unknown location in Russia.