The United States Ambassador to New Zealand says President Donald Trump's tweets are not to blame for heightened tensions with Kim Jong-un - and Kiwis need to realise the direct danger from a nuclear-armed North Korea.

At a recent event Ambassador Scott Brown was told by a couple of people that Trump's tweets were instigating problems with North Korea. He told Fairfax he didn't accept that view.

"I said, 'I'm sorry, Sir, with all due respect, it's not my President's tweets, it's the fact you have a leader, an isolated, desperate leader who's lobbying ICBMs [intercontinental ballistic missiles] and threatening to nuclearise them...let's not get sidetracked here'," Brown said.

"You have somebody who is out there stirring the pot, has some new toys, some new weapons and wants to go out and basically sabre-rattle. And I think it's wrong."

The United States Ambassador Scott Brown. (Photo \ Mark Mitchell)

Tensions between the US and North Korea have built after Pyongyang tested missiles and a nuclear device. US Secretary of State Rex Tillerson, speaking at a press conference in Beijing, said the US had direct lines of communication to North Korea and was "probing" to find ways to resolve growing tensions between the countries.

"We've made it clear that we hope to resolve this through talks," Tillerson said. "I think the most immediate action that we need is to calm things down."

However, a day later Trump tweeted his view that Tillerson should "save his energy".

"I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man," Trump tweeted on Sunday. "...Save your energy Rex, we'll do what has to be done!"

He followed up later in the day.

"Being nice to Rocket Man hasn't worked in 25 years, why would it work now? Clinton failed, Bush failed, and Obama failed. I won't fail."

Little Rocket Man is Trump's nickname for North Korean leader Kim Jong Un.

I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man...

— Donald J. Trump (@realDonaldTrump) October 1, 2017

In his interview with Fairfax, Brown said many New Zealanders didn't understand the true threat from North Korea.

"They understand, 'Gosh, we're so far away and it really doesn't affect us'. Well, it does if he decides to drop a hydrogen bomb in the Pacific Ocean.

"The fallout could come here. It could affect the fishing and all the sea life. It'd dramatically affect climate and economy and the ability to travel freely in that region without being contaminated. So, yeah, it does affect New Zealand."

Brown, a former Massachusetts Republican senator, was one the first ambassadors in the Donald Trump Administration to be confirmed, and arrived in New Zealand in June. He is a former male model and posed nude when he won Cosmopolitan magazine's "America's sexiest man" competition.