Rather than firing a bomb directly at an American city, the dictatorship could detonate a bomb high in the atmosphere, unleash a pulse of radio waves which could destroy electronics across America.

The warning comes just as Pyongyang upped the rhetoric once again, saying nuclear war might break out at any moment.

Dr William Graham and Dr Peter Vincent Pry from the EMP Commission describe the attack in a new paper titled ‘North Korea Nuclear EMP Attack: An Existential Threat.’

They say that the bomb would be detonated around 18 miles up, or possibly even higher, with the goal of ‘frying’ the electric power grid.

The researchers write, ‘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.’

The researchers write, ‘With the development of small nuclear arsenals and long-range missiles by new, radical US adversaries, beginning with North Korea, the threat of a nuclear EMP attack against the US becomes one of the few ways that such a country could inflict devastating damage to the United States.’

The research comes at a heightened point of tension between the two countries.

Although Donald Trump has recently said that diplomacy will not work with ‘Rocket Man Kim’, on Tuesday the U.S. said it is not ruling out the eventual possibility of direct talks with the hermit state.