DUBAI, United Arab Emirates (AP) — Iran has enough highly enriched uranium to build "several" nuclear weapons if it chooses, the United Nations' top nuclear official is now warning. But diplomatic efforts aimed at again limiting its atomic program seem more unlikely than ever before as Tehran arms Russia in its war on Ukraine and as unrest shakes the Islamic Republic.

The warning from Rafael Mariano Grossi of the International Atomic Energy Agency, in response to questions from European lawmakers this week, shows just how high the stakes have become over Iran's nuclear program. Even at the hei...