WASHINGTON - US National Security Agency (NSA) is implementing new security measures after disclosures made by former contractor Edward Snowden put the agency under the spotlight, Deputy Defense Secretary Ashton Carter said Thursday.

Carter made the remarks at the Aspen Security Forum held in Colorado. He said systems administrators like Snowden must now work with a colleague when accessing sensitive, compartmented intelligence.

He said the "two-man rule" is based on the model of how nuclear weapons are handled, which requires two computer systems administrators to be working simultaneously when they are inside systems that contain highly classified material.

Furthermore, Carter said, the NSA is now working to limit access to sensitive data.

"In an effort for those in the intelligence community to be able to share with each other, there was an enormous amount of information concentrated in one place. That's a mistake," he said. "The loading of everything onto a server creates a risk."

According to NSA Director Keith Alexander, Snowden accessed much of the information on a single internal site designed to share information.