The US president also criticised the Iran nuclear deal as "an embarrassment to the United States"
US President Donald Trump has said the US will have no choice but to "totally destroy" North Korea if his country has to defend itself or its allies from an attack.
This afternoon, President Trump addressed the UN General Assembly in New York - his first address to the annual gathering of world leaders.
After reiterating his 'America First' approach, the US President turned to some of his favoured international topics - including migration, North Korea and Iran.
On the subject of North Korea, he hit out at leader Kim Jong-un as a 'rocket man on a suicide mission'.
While welcoming recent sanctions against the secretive state, he told delegates: "It is an outrage that some nations would not only trade with such a regime, but would arm, supply and support such a country that imperils the world with nuclear conflict.
"If [the US is] forced to defend itself for its allies, we will have no choice but to totally destroy North Korea. 'Rocket man' is on a suicide mission for himself, and for his regime. The United States is ready, willing and able - but hopefully this will not be necessary.
"That's what the United Nations is all about - that's what the United Nations is for. Let's see how they do. It is time for North Korea to realise that the denuclearisation is it's only acceptable future."
President Trump also called on the world to confront what he called a 'reckless regime' in Iran.
He argued: "The Iranian government masks a corrupt dictatorship behind the false guise of a democracy. It has turned a wealthy country, with a rich history and culture, into an economically depleted rouge state whose chief exports are violence, bloodshed and chaos. The longest suffering victims of Iran's leaders are in fact it's own people."
The US leader has been a frequent critic of the international deal over Iran's nuclear programme, despite a watchdog recently suggesting the Middle Eastern state is sticking to its obligations.
Trump returned to the topic during the speech today, suggesting: "We cannot let a murderous regime continue these destabilising activities while building dangerous missiles - and we cannot abide by an agreement if it provides for the eventual construction of a nuclear programme.
"The Iran deal was one of the worst and most one-sided transactions the United States has ever entered into - frankly that deal is an embarrassment to the United States, and I don't think you've heard the last of it, believe me."
On the UN itself, President Trump said the US bears 'an unfair cost burden' of the organisation's budget.
He observed: "To be fair, if it could actually accomplish all of its stated goals - especially the goal of peace - this investment would easily be well worth it.
"Major portions of the world are in major conflict, and some in fact are going to hell. But the powerful people in this room, under the guidance and auspices of the United Nations, can solve many of these vicious and complex problems."
Concluding his speech, President Trump told delegates that "we will fight together, sacrifice together and stand together".