Two members of the now disbanded congressional Electromagnetic Pulse (EMP) commission told a recent House Homeland Security subcommittee hearing that a nuclear EMP attack remained the "biggest threat" facing the US today.
The powerful weapon has the potential to shut down America's power grid and kill millions of people.
North Korea has tested several intercontinental ballistic missiles this year and claimed to have successfully tested a miniaturised hydrogen bomb on September 3.
The secretive state claimed such a bomb could be detonated at high altitudes for "super-powerful EMP attack according to strategic goals".
Chairman of the now defended EMP commission William Graham and its former chief of staff Peter Vincent Pry told the hearing an EMP attack would be devastating.
"The result could be to shut down the US electric power grid for an indefinite period, leading to the death within a year of up to 90 per cent of all Americans," they warned.
A nuclear EMP attack destroys electronics and blackout supplies, meaning everyday modern day activities would grind to a standstill.
The hearing also heard how the US missile defence system may not adequately protect the country from a North Korean missile.
"Current US BMD systems are not arranged to defend against even a single ICBM that approaches the United States from over the South Polar region, which is the direction toward which North Korea launches its satellites," the committee was told.
Nuclear disarmament campaigner John Hallam said the EMP threat is real and is more or less as bad as it's said to be.
