US President Donald Trump threatened to respond with "fire and fury" if North Korea does not cease its threats against the US.

"North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen. He has been very threatening ... and I said, they will be met with fire, fury, and frankly power the likes of which this world has never seen before," Trump told reporters during his vacation at his New Jersey golf club Tuesday.

The president's remarks followed reports that North Korea has produced a nuclear warhead small enough to fit onto an ICBM, which could strike parts of the US.

The assessment on North Korea's latest breakthrough puts the US within range of a North Korean nuclear strike if the rogue regime places a nuclear warhead on an Intercontinental Ballistic Missile (ICBM).

Last month, a top US general stated that North Korea "clearly" had the capability to strike parts of the US with an ICBM. The rogue nation has repeatedly test-fired ballistic missiles recently.