Donald Trump threatened to “totally destroy North Korea” if the US is forced to defend itself or allies against aggression in a strongly worded address to the general assembly of the United Nations.
Mr Trump, speaking in his home city of New York, also took aim at Iran in his speech at the world body’s headquarters.
The US president described North Korean leader Kim Jong Un as a “rocket man on a suicide mission” following a series of weapons tests by the Pyongyang regime.
He also said the Iranian government was running an “economically depleted rogue state” whose chief export is violence.
Mr Trump signalled a stronger approach to Tehran, questioning the 2015 nuclear deal with Iran struck by his predecessor.
He said world leaders “cannot abide” by the agreement if it “provides cover” for Iran to eventually build its nuclear programme.
The US administration last week extended sanctions relief to Iran, avoiding imminent action that could implode the landmark agreement.