The former prime minister, one of Australia's most-respected foreign policy thinkers and a strong advocate for a more independent foreign policy, has disagreed strongly with the language and approach being taken the US President Donald Trump towards the rogue state.

On Friday, US President Donald Trump reiterated his bellicose warning to North Korea, suggesting that his threat to unleash "fire and fury" may not have gone far enough.

"Maybe it wasn't tough enough," Trump said during a lengthy exchange with reporters at his golf club in Bedminster, New Jersey.

Mr Keating said his criticism could be extended to Australia's pledge to enter any potential conflict between the US and North Korea. He also disagreed with former prime ministers Kevin Rudd and Tony Abbott that Australia should pursue a missile defence system against North Korea's intercontinental ballistic missiles.

His comments about the growing tensions on the Korean peninsula come on the same day that Prime Minister Malcolm Turnbull declared Australia would assist America if it was attacked by North Korea.

"If there is an attack on the United States by North Korea, then the ANZUS treaty will be invoked and Australia will come to the aid of the United States," Mr Turnbull said. This would be only the second time the ANZUS treaty had been invoked.

Speaking ahead of a national security briefing with Defence Minister Marise Payne and Defence Force chief Mark Binskin, Mr Turnbull highlighted the UN Security Council's recent imposition of harsher sanctions on North Korea which, significantly, were backed by China and Russia.

"As I discussed with Vice-President Pence last night [Thursday], both the United States and Australia are committed to resolving this situation on the Korean Peninsula, to bringing the North Korean regime to its senses through diplomatic and economic means. We stand shoulder-to-shoulder with the United States."

US President Donald Trump has threatened to unleash "fire and fury" on the rogue state and the North Korean regime has, in turn, warned it would attack the US Pacific territory of Guam, home to a major airforce base.

Mr Keating decided to speak publicly after being contacted by Fairfax Media and his views will be expanded in a major essay for a new magazine, Australian Foreign Affairs, to be published in October.

"I have long believed, especially after the unprovoked Western attack on Iraq and the ransacking of the Gaddafi regime in Libya, that North Korea would not desist from the full development of its nuclear weapons program, despite threats and sanctions from the West and even from China," he said

"I said in April, we should regard North Korea as a full and capable nuclear weapons state – a state that would, in future, need to be contained, in the way the Soviet Union was contained during the Cold War. Developments since April have only confirmed my view."

"More than that, it may be, that because the development of nuclear weapons in North Korea has, in a sense, become the raison d'etre of the state, were Kim Jong-Un and his generals to agree to the West's demands, they may not politically survive that acquiescence."

"The moral in this is that all nuclear proliferation is bad and dangerous, particularly in the hands of outlier regimes like North Korea. We knew this from the moment the Manhattan Project succeeded in 1945."

When asked if a missile shield was an option that Australia should pursue to protect the mainland, Mr Keating's response was blunt.

"I think this is more than debatable. The offending missiles would approach their targets at something like Mach 20, a phenomenal speed. We could never know, until the fatal event, whether a missile defence system would effectively work, or work in respect of each and every missile," he said.

"A more worldly and competent foreign and defence policy is by far the preferred first line of defence – rather than the default position of relying on expensive but problematic hardware."

Mr Turnbull also disagreed with Mr Abbott and Mr Rudd - who have both told Fairfax Media in the last four weeks that Australia should pursue missile defence - on the need for such a shield.

He said on Friday the current advice from Defence was that the terminal high altitude area defence [THAAD] system "is designed to provide protection for relatively small areas against short to intermediate range missiles".

Former US Ambassador Kim Beazley said the prime minister had responded to a hypothetical situation when discussing whether to invoke the ANZUS alliance and not "an automatic commitment" but is "as close to automatic as we can get".

We have a commitment there which is as close to automatic as we can get.

"It does not arise from the ANZUS alliance but from the United Nations. We are still technically at war on the Peninsula but we are signatories to an Armistice, agreed with the UN," he said.

Greens leader Richard Di Natale said "the last thing we need here is a Prime Minister backing an unhinged and paranoid leader into a conflict that could potentially end life on Earth as we know it".

He called on Mr Turnbull to tell the President to "back off".

"If there was an ever a clearer example of why Australia needs to ditch the US alliance and forge an independent, non-aligned foreign policy, this is it. Malcolm Turnbull now needs to pick up the phone, he needs to talk to Donald Trump and urge him to de-eascalate."

Defence analysts believe North Korea's longest-range missiles could reach Australia. Foreign Minster Julie Bishop has said North Korea's ICBMs pose an "existential threat" to Australia, though we are not a primary target.

The US, Japan, western Europe, Israel and other nations have deployed missile defence.