U.S. President Donald Trump warned on Tuesday that the United States will be forced to "totally destroy" North Korea unless Pyongyang backs down from its nuclear standoff, mocking North Korean leader Kim Jong-un as a "rocket man" on a suicide mission.

Loud murmurs filled the green-marbled UN General Assembly hall when Trump issued his sternest warning yet to North Korea, whose ballistic missile launches and nuclear tests have rattled the globe.

Unless North Korea backs down, he said, "We will have no choice than to totally destroy North Korea."

"Rocket man is on a suicide mission for himself and his regime," he said.

A junior North Korean diplomat remained in the delegation's front-row seat for Trump's speech, the North Korean UN mission said.

In his first appearance at the annual gathering of world leaders, Trump used a 41-minute speech to take aim also at Iran's nuclear ambitions and regional influence, Venezuela's collapsing democracy and the threat of Islamist extremists. He also criticized the Cuban government.

Singles out countries including North Korea, Iran, Syria 9:08

But his strongest words were directed at North Korea. He urged United Nations member states to work together to isolate the Kim government until it ceases its "hostile" behaviour. He said North Korea's pursuit of nuclear weapons and ballistic missiles "threatens the entire world with unthinkable cost of human life."

We must not sleepwalk our way into war. - Antonio Guterres, UN secretary-general

In what may have been a veiled prod at China, the North's major trading partner, Trump said: "It is an outrage that some nations would not only trade with such a regime but would arm, supply and financially support a country that imperils the world with nuclear conflict."

Then turning to Iran, Trump said the 2015 nuclear deal negotiated by his predecessor, Barack Obama, was an "embarrassment" and hinted that he may not recertify the agreement when it comes up for a mid-October deadline.

"I don't think you've heard the last of it," he said.

He also called Iran an "economically depleted rogue state" that exports violence.

U.S. president decries Iran regime at United Nations 2:05

'America's interests above all else'

Reading carefully from a script, Trump promised the United States military would soon be the strongest it has ever been.

The speech marked his latest attempt to lay out his 'America First' vision for a U.S. foreign policy aimed at downgrading global bureaucracies, basing alliances on shared interests, and steering Washington away from nation-building exercises abroad.

North Korea's UN ambassador, Ja Song Nam, leaves his seat prior to Trump's arrival. (Shannon Stapleton/Reuters)

Trump, who entered the White House eight months ago, told world leaders at the 193-member global body that the U.S. does not seek to impose its will on other nations and will respect other countries' sovereignty, despite ramping up U.S. military activity in several theatres of war since taking office.

"I will defend America's interests above all else," he said. "But in fulfilling our obligations to other nations, we also realize it's in everyone's interest to seek a future where all nations can be sovereign, prosperous and secure."

U.S. president demands better trade deals for Americans 1:02

The U.S. president also managed to address the ongoing turmoil in Venezuela, calling the situation there "completely unacceptable.

"We cannot stand by and watch," he said.

Call for 'statesmanship'

Shortly before Trump's speech, UN Secretary-General Antonio Guterres appealed from the General Assembly lectern for statesmanship to avoid war with North Korea.

"This is the time for statesmanship," said the former prime minister of Portugal. "We must not sleepwalk our way into war."

Prime Minister Justin Trudeau, who was asked to comment at the same time Trump was speaking, said he shares the concern over the "reckless" behaviour of the North Korea regime.



Trudeau said he thought working with partners and allies "in the region and around the world, including China, Japan, South Korea and the United States, is the best way to de-escalate this situation, which is a danger not just to the region, but to global peace."

Defence Secretary Jim Mattis said after the address that the U.S. wants to find a diplomatic solution to the North Korea situation.

"We are dealing with the North Korea situation through the international process and we will continue to do so. Secretary Tillerson is leading the effort and we will hopefully get this resolved through diplomatic means," Mattis said before the start of a meeting with Romania's defence minister.

The UN Security Council has unanimously imposed nine rounds of sanctions on North Korea since 2006 and Guterres appealed for the 15-member body to maintain its unity on North Korea.

Trump has warned North Korea that military action was an option for the United States as Pyongyang has carried out a series of tests toward developing the ability to target the United States with a nuclear-tipped missile.