Trump tells UN he has 'big decision' on whether to 'annihilate' Iran or make peace deal

President Donald Trump has told the United Nations General Assembly he faces a "big decision" on whether to strike Iran again or pursue a peace deal.

A single member of Iran's delegation watched on during the president's speech in New York, in which he said he could "annihilate" the Islamic Republic if the conflict went unresolved.

Before a standing-room-only audience, Trump also rejected "global government", vowed to broker peace between Russia and Ukraine and ensure the US wins the artificial intelligence race.

His tone contrasted with remarks earlier by UN Secretary General António Guterres, who warned global divisions were deepening and underscored the "interdependence" of the world's peoples.

Trump's speech on Tuesday came on a day of high-level diplomacy at the United Nations. He's meeting more than a dozen world leaders as wars in the Middle East and Ukraine test his foreign policy agenda.

He began by touting his accomplishments on the economy, immigration, the border and tackling violent crime, in remarks that sounded more pitched to voters in November's US midterm elections than the diplomats in Manhattan.

He spent much of his address justifying the war with Iran, which has spiked global oil prices while dragging down his approval ratings since the US and Israel launched the military action in February.

Trump argued that the conflict had prevented Tehran from obtaining a nuclear weapon and demonstrated the value of what he described as peace through strength - ultimatums rather than deal-making or compromise.