Iranian President Mahmoud Ahmadinejad used a UN conference in New York City yesterday to blast the United States for threatening to use atomic weapons, triggering a walkout by US and other delegates.
"Regrettably, the government of the United States has not only used nuclear weapons but also continues to threaten to use such weapons against other countries, including Iran," Mr Ahmadinejad told the opening session of a meeting reviewing the landmark Nuclear Non-Proliferation Treaty (NPT).
US Secretary of State Hillary Clinton was due to speak later in the day, with the US-Iranian nuclear standoff clearly looming large over the conference, which runs through May 28.
Mrs Clinton had warned on Sunday that Iran would try to divert attention at the crucial meeting from its violations of its obligations under the NPT which it has signed along with 188 other states.
Mr Ahmadinejad said having nuclear weapons was "disgusting and shameful, and even more shameful is the threat to use or to use such weapons".
In Washington, the Defence Department was set to release previously classified statistics on the size of the US nuclear arsenal.
This is part of a US drive to prove it is serious about disarmament and transparency about its nuclear weapons.
Washington has launched various initiatives recently to give weight to President Barack Obama's vow to work for a world free of nuclear weapons.
The NPT review is an attempt to tighten up the non-proliferation regime, which is based on monitoring national nuclear programs as well as promoting both disarmament and the peaceful use of atomic energy.
In his 35-minute speech, Mr Ahmadinejad called for the United States to be suspended from the UN atomic watchdog's executive board over its threats to use nuclear weapons.
"How can the United States be a member of the board of governors (of IAEA, the International Atomic Energy Agency) when it used nuclear weapons against Japan" and also used depleted uranium weapons in the war against Iraq, he said.
Besides the United States, fellow nuclear powers Britain and France walked out. Non-nuclear states which also left included Germany, Finland, the Czech Republic and Morocco, according to a Western diplomat.
Mr Ahmadinejad also called for an independent body to set a deadline for the elimination of all nuclear weapons, in a wide-ranging speech on saving the non-proliferation regime from what he said were abuses by nuclear powers.