US Secretary of State Hillary Clinton and Iranian President Mahmoud Ahmadinejad entered into a war of words, calling the other nation's nuclear capability as the principal threat to international stability.
Ahmadinejad fired the first salvo at a special UN conference on the global nuclear non-proliferation regime on Monday, accusing the US of leading a skewed international system that seeks to deny peaceful nuclear power to developing nations while allowing allies such as Israel to stockpile atomic arms.
Demanding that the world's nuclear-weapons states agree to a clear timetable for the disbandment of their arsenals, Ahmadinejad said: "The possession of nuclear bombs isn't a source of pride; it is disgusting and rather shameful."
"And even more shameful is the threat to use or to use such weapons, which isn't even comparable to any crime committed throughout the history."
British, American and French diplomats walked out of Ahmadinejad's speech in quick succession about 10 minutes into its delivery.
Clinton followed in the afternoon saying Iran "will do whatever it can to divert attention from its own record and to attempt to evade accountability," and dubbing Ahmadinejad's comments as "the same tired faults and sometimes wild accusations" against the United States and other countries.
Iran has continuously defied the UN's International Atomic Energy Agency and its Security Council, she said, adding that Iran was the "only country in this hall that has been found by the IAEA board of governors to be currently in non-compliance with its nuclear safeguards obligations."
She called on Ahmadinejad and his regime "to join with all the other delegations represented at this meeting to go ahead and fulfil our international obligations and work toward the goal of a safer world."
Clinton also declared that the US was announcing the size of its nuclear arsenal, as well as the number of atomic weapons destroyed since 1991. The Pentagon later said the US had a total of 5,113 warheads in its stockpile, plus a few thousand more that had been retired but still needed to be dismantled.
It was the first time the US has disclosed those figures, which had been previously regarded as highly classified.
Obama released a statement claiming that the course of Iran's nuclear work could define whether the Nuclear Nonproliferation Treaty survives into the 21st century.
"Over the coming weeks, each of our nations will have the opportunity to show where we stand. Will we meet our responsibilities or shirk them?" Obama said in a statement.
"In short, do we seek a 21st century of more nuclear weapons or a world without them?"