U.S. Defense Secretary Leon Panetta said Thursday that he was deeply worried about the risk of a major cyber attack on the United States that could paralyze the country.

In response to questions following a speech to more than 1,200 people at the University of Louisville, Kentucky, Panetta said what keeps him awake at night is the possibility of such an attack.

"We are literally getting hundreds or thousands of attacks every day that try to exploit information from various U.S. agencies or departments," Panetta was quoted by the American Forces Press Service as saying. There are also many targets beyond the government, he said.

The attacks could bring down power grids and affect U.S. governmental and financial systems, literally paralyzing the country, he said.

Panetta said as the United States remains "indispensable to a stable and secure world," it must make maintaining its military might a priority and be more prepared for potential mass cyber attacks.

After the end of the Iraq war, the United States still faces many security challenges. Terrorists in Somalia, Yemen and North Africa continue to plot attacks on U.S. targets, he said.

"We must continue to invest in new capabilities like cyber and unmanned systems, space, and the continued growth of special operations forces," Panetta said.

He also called on the U.S. government to take on fiscal responsibility to deal with the debt issue, as an uncontrolled budget will deprive the defense department of the necessary resources for fending off potential attacks.