A clash between Iran and the United States and a breakthrough announcement by Washington Monday dominated the opening session of the three-week-long review of the 40-year-old Nuclear Non-Proliferation Treaty (NPT) at the UN Headquarters in New York.

U.S. Secretary of State Hillary Clinton vowed the departments of defense and energy were releasing the long-secret number of nuclear weapons in the U.S. arsenal and the number dismantled since 1991.

As promised, the Defense Department later said it had 5,113 nuclear warheads in the arsenal.

Iranian President Mahmoud Ahmadinejad, who led off the list of individual nations to speak, focused immediately on what he described as an inherent right of security threatened by the United States.

However, UN Secretary-General Ban Ki-moon criticized Iran for its non-compliance with the International Atomic Energy Agency (IAEA) and the UN Security Council and not accepting a nuclear fuel exchange plan.

It was part of his plea to nations to make nuclear disarmament a reality.

Ban then left the dais where he normally sits during assembly sessions.

Technically, this was not a 192-member assembly session but a meeting of parties to the treaty. Still, it was seen as a snub.

France boycotted Ahmadinejad's speech, and representatives of eight other nations, namely Austria, Belgium, Britain, the Czech Republic, Germany, Italy, the Netherlands and the United States, walked out while he was speaking.

Before he began his formal remarks, the Iranian president interjected a reply to Ban.

"The secretary-general said that Iran must accept the fuel exchange and that the ball is now in Iran's court," Ahmadinejad said. "Well, I would like to tell you and inform him as well that we had accepted that from the start, and I would like to announce once again that is an accepted deal. Therefore, we have now thrown the ball in the court of those who should accept our proposal and embark on cooperation with us."