"This includes nuclear employment of any scale, and it includes high-consequence attacks of a strategic nature that use non-nuclear means," a senior defense official told journalists.

The unclassified version of the US military's Nuclear Posture Review also contains a stark warning for North Korea's Kim Jong Un against employing the country's growing atomic arsenal.

"Any nuclear attack by North Korea against the United States or its Allies and partners is unacceptable and will result in the end of that regime. There is no scenario in which the Kim regime could employ nuclear weapons and survive," the strategy says.

Kim has declared the country an "irreversible" nuclear power, effectively ending negotiations over his banned arms programs.