John Bolton admitted there was a huge risk of South Korea being hit by its despotic neighbour in retaliation for any US military action, putting hundreds of thousands in peril.
But he said the President would not be able to ignore the threat for much longer as Pyongyang’s military ambitions showed no sign of ending.
Speaking at a Republican dinner in Asheville, North Carolina, he said “nobody” wanted World War 3 to break out.
But he claimed: “I will just say this. The president of the United States’ first duty is to protect Americans.
“You have to make the choice at some point whether the risks are greater in preventing North Korea from getting the capability of blackmailing or actually attacking the United States against the dangers of, the consequences of, a pre-emptive strike.”
Slamming previous failed attempts to negotiate with Kim Jong-un’s regime, he claimed the time for talking was nearing an end.
And he warned the hermit state could sell its deadly weaponry to other despotic regimes like Iran, ramping up the threat to the west.
He told the audience: “Whatever North Korea has today, Iran could have tomorrow by writing a large enough cheque.”
And he dismissed claims that Pyongyang could be contained with Cold War-style tactics.
Mr Bolton said: “It’s a myth to think that a regime as irrational in our terms as North Korea or as extreme ideologically as Iran are going to be deterred in the same way.
“I just think as citizens we’ve all got a responsibility to think about this, because if we don’t stop nuclear proliferation here, we’re not going to stop it anywhere.”
Mr Bolton has previously warned the US must destroy Pyongyang’s military capabilities after it launched a missile capable of striking the US.
His latest comments came as the North warned the US to prepare for “nuclear war”.
A state-run newspaper said plans for a sea blockade “cannot be tolerated”.
It warned: “A naval blockade is an act of wanton violation of the sovereignty and dignity of an independent state and an act of war of aggression which cannot be tolerated.
“The gang of Trump is taking extremely dangerous and big step towards the nuclear war by recklessly seeking the naval blockade against our country, neglecting the strategic prestige of our country that has achieved the great historic cause of completing the state nuclear force.”
The US and South Korea have taken part in a series of joint military drills in recent days as a show of defiance to the North.
The military training took place between Tuesday and Friday and is said to have replicated how weapons of mass destruction would be destroyed in the hermit state.
US Defence Secretary James Mattis has suggested a “ground invasion” is required in order to stop the threat posed by Kim’s sabre-rattling regime.