The United States faces a growing threat of a "cyber-Pearl Harbor" and has drafted new rules for the military that would enable it to move aggressively against digital attacks, Defense Secretary Leon Panetta said on Thursday.

The amended rules of engagement underline the need to defend Defense Department computer networks, "but also to be prepared to defend the nation and our national interests against an attack in or through cyberspace", he said.

Citing a mounting cyber danger that could cripple the country's vital infrastructure, Panetta told an audience in New York: "We won't succeed in preventing a cyber attack through improved defenses alone.