The United States faces "the cyber equivalent of the World Trade Center attack" unless urgent action is taken, a former U.S. intelligence chief warns.

John "Mike" McConnell, who served as director of the National Security Agency under President Clinton and then as director of national intelligence under George W. Bush and President Obama, told the Financial Times (subscription required) that such an attack would cripple the nation's banking system, power grid, and other essential infrastructure.

"We have had our 9/11 warning. Are we going to wait for the cyber equivalent of the collapse of the World Trade Centers?" McConnell said, referring to attacks on the Web sites of major banks and a cyberattack earlier this year that rendered two-thirds of the computers at Saudi Arabian oil company useless.

U.S. officials have blamed Iran for creating the Shamoon virus, which was responsible for a cyberattack that infected more than 30,000 computers at Saudi Aramco and Qatar's natural gas firm Rasgas in mid-August. McConnell echoed comments made in October by Defense Secretary Leon Panetta, who warned that the U.S. was facing the possibility of a "cyber-Pearl Harbor" perpetrated by foreign hackers.

"All of a sudden, the power doesn't work, there's no way you can get money, you can't get out of town, you can't get online, and banking, as a function to make the world work, starts to not be reliable," McConnell said. "Now, that is a cyber-Pearl Harbor, and it is achievable."

McConnell expressed doubt that Iran or any terrorist group could mount such an attack but said it was only a matter of time before they had the capability.