Twitter was left terrified after US President Donald Trump threatened to "totally destroy" nuclear-armed North Korea in a fiery maiden speech at the United Nations general assembly. Referring to Kim Jong-un as "Rocket Man", Trump said the North Korean leader "is on a suicide mission for himself and for his regime" through his "reckless" pursuit of nuclear weapons and ballistic missile tests.

"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," Trump said, seemingly referring to Pyongyang's closest trade partner China.

"No nation on Earth has an interest in seeing this band of criminals arm itself with nuclear weapons and missiles. The United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea."

The president also criticised Iran as a "reckless regime" and an "economically depleted rogue state" whose chief exports are "violence, bloodshed and chaos." He slammed 2015 nuclear agreement with Tehran as an "embarrassment to the United States" and "one of the worst and most one-sided transactions the United States has ever entered into."

"I don't think you've head the last of it," he continued. "Believe me."

Trump also pledged to stop "radical Islamic terrorism" and said the US was working together with its allies "to crush the loser terrorists and stop the reemergence of safe havens they use to launch attacks on all of our people."

"Major portions of the world are in 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," Trump said.

The president's remarks received a mixed reception from world leaders and sparked fear and fierce criticism on Twitter for what many described as "war mongering." While Trump's supporters and allies praised his speech as "tough" and "courageous", critics said his comments only "further isolates the United States."

Senator Dianne Feinstein said in a statement: "The goals of the United Nations are to foster peace and promote global cooperation. Today, the president used it as a stage to threaten war."

One Twitter user wrote: "I can't believe you said this INSANE war mongering nonsense at the UN. The world is laughing at us. It's as if you want a nuclear war."

"As an American I felt ashamed to watch you speak in front of the world," another tweeted. "You told the world you would commit mass genocide in North Korea. Even your Chief of Staff couldn't bear watching.

"You bought right into exactly what Kim Jong-Un wants. He wants his citizens to look at us as the enemy and now they certainly do."

One person described Trump's first UN speech as "despicable trash."

He's standing in front of an international diplomatic organization arguing nationalism and war," the Twitter user wrote. Another called Trump "the most ill-informed, under-prepared, ethically-challenged and psychologically ill-equipped President in US history."

Trump addresses the 72nd United Nations General Assembly at UN headquarters in New York. REUTERS/Eduardo Munoz