A fresh diplomatic confrontation over Iran's nuclear programme unfolded at the United Nations Security Council as US Ambassador Mike Waltz accused Tehran of failing to cooperate with the International Atomic Energy Agency (IAEA). Addressing the council, Waltz delivered a strong warning, declaring that the United States would never accept a nuclear-armed Iran. He also challenged Tehran to provide answers to the nuclear watchdog's outstanding questions. IAEA Director General Rafael Grossi raised concerns over the agency's inability to verify the status of Iran's previously declared nuclear material, including approximately 440 kilograms of highly enriched uranium. He called for the necessary information and access to nuclear facilities so inspectors can resume verification. The inspection dispute comes amid wider tensions following military strikes on Iranian nuclear facilities in 2025 and 2026. Iran, meanwhile, has criticised the US and its allies, arguing that the attacks disrupted the inspection process. What exactly did Mike Waltz tell Iran? Why is the IAEA seeking access to nuclear sites? And what does the 440-kilogram uranium stockpile mean for international security?