Speaking at a forum held by the Hudson Institute think tank, Air Force General John Hyten said the US must look at North Korea developing the capability as a “matter of when not if.”
North Korea’s current missiles are believed the be inaccurate as they have struggled to develop a guidance system that survives orbital re-entry.
The heat of re-entry can warp the missile and render it totally inaccurate.
But Mr Hyten added that it was only a matter of time before North Korea developed the technology: “If you’re going down that path, you’ll eventually figure it out. You will.
“So we have to assume, and as commander of Strategic Command, I have to assume, that they have the bomb and they will have the capability to deploy it on an ICBM.
“And I have to figure out how to respond if asked by the President of the United States.
“If they want to attack the United States with nuclear weapons, it is not going to work out well for North Korea,” Hyten said, adding that if such an attack occurred, “the response is going to be overwhelming.”
Mr Hyten also said he is confident that the anti-ballistic missile shield Ground-Based Midcourse Defence (GMD) can deflect a North Korean ICBM launched at US territory.
The £29billion ($40billion) programme was established in 1999, it has had 19 tests and failed nine of them – meaning it has a success rate of around 50 per cent.
Mr Hyten continued: “Could it be better? Yes.
“But I am confident today that if something happened, [US Northern Command head, Air Force Gen Lori Robinson] has the ability with the fielded forces we have to defend against ballistic missile attack by North Korea.”
It comes amid rising tensions on the Korean peninsula after repeated nuclear tests by Kim Jong-un.
Last Friday North Korea launched a missile over Japan and earlier this month the hermit kingdom detonated a hydrogen bomb which sparked a 6.3 magnitude earthquake.