UNITED NATIONS – Secretary of State Hillary Clinton and the United Nations’ top leadership used a high-level nuclear conference Monday to publicly scold Iranian President Mahmoud Ahmadinejad for his country’s defiance of U.N. resolutions, while the United States and its European allies staged a walkout to protest Tehran’s nuclear stance.

In an afternoon address to a conference to review the 40-year-old nuclear Non-Proliferation Treaty, Clinton responded sharply to a fiery speech at midday in which Ahmadinejad blamed the United States for a global nuclear arms race and dismissed the prospect of “nuclear terrorism” — identified by President Obama as the main atomic threat facing the world.

“Iran’s president offered the same tired, false and sometimes wild accusations against the United States and other parties at this conference,” Clinton said. “But that’s not surprising. Iran will do whatever it can to divert attention away from its own record and to attempt to evade accountability.”

She backed U.N. Secretary General Ban Ki-moon’s earlier statement that “the onus is on Iran” to prove its nuclear program is entirely peaceful.

“So far, it has failed to meet its burden,” she said, adding that Iran is the only country at the conference that has been found by the International Atomic Energy Agency “to be currently in noncompliance with its nuclear safeguard obligations.”

Iran “has defied the Security Council and the IAEA and placed the future of the nonproliferation regime in jeopardy,” Clinton said. “But Iran will not succeed in its efforts to divert and divide.”

U.N. PRESSURES TEHRAN

Ban and the chief U.N. nuclear arms watchdog, Yukiya Amano, also blamed Ahmadinejad for provoking the diplomatic standoff over Tehran’s nuclear program.

The remarks by Ban constituted an extraordinary rebuke of a world leader in the U.N. General Assembly chamber and reflected mounting concern that Tehran’s nuclear policy threatens to undermine the review conference of the NPT.

“I call on Iran to comply fully with Security Council resolutions and cooperate fully with the International Atomic Energy Agency,” Ban said at the opening of the nearly month-long conference. “Let us be clear: The onus is on Iran to clarify the doubts and concerns about its program.”

Ban urged the Iranian leader to “engage constructively” in international talks aimed at resolving Iran’s nuclear standoff with the U.N. Security Council.

He said Tehran should accept a proposal by the IAEA to ship Iran’s nuclear fuel abroad in exchange for a more purified form of uranium to power the country’s medical research reactor. The plan is backed by the United States, Russia, China and other key powers.

In a rare breach in protocol, Ban left the General Assembly hall for another meeting shortly before Ahmadinejad — the only head of state to address the nuclear conference — delivered his speech. When Ahmadinejad took to the podium, he responded directly to Ban.

“The secretary general said that Iran must accept the fuel exchange and that the ball is now in Iran’s court,” he said.

“Well, I’d like to tell you and inform him as well that we’d accepted that from the start, and I’d like to announce once again that (it 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.”

Iran has repeatedly said it is willing to discuss the fuel swap, only to reverse course. It has recently engaged in preliminary discussions with Turkey and Brazil on a plan to revive talks on the deal.

But the United States and its European partners have expressed skepticism, saying that Iran’s latest interest in talks is aimed at stalling a U.S.-backed initiative to impose a fourth round of U.N. sanctions on Tehran. Russia and China have cited Iran’s refusal to accept such a deal in justifying their decision to pursue sanctions.

BLAMING THE U.S.

The Iranian leader used his speech to deliver a fierce attack on the United States, saying it introduced nuclear weapons to the world and is fueling the global nuclear arms race.

He accused the United States and other nuclear states of manipulating the international arms control system, including the IAEA, to preserve its nuclear privileges while pressuring non-nuclear states to give up their rights to produce nuclear fuel for energy purposes.

“Those who committed the first atomic bombardment are considered to be among the most hated individuals in human history,” he said. “Regrettably, the government of the United States has not only used nuclear weapons, but it also continues to threaten to use such weapons against other countries, including Iran.”

The IAEA’s director general, Amano, made it clear that he is not satisfied with Iran’s efforts to resolve the issue. In his address to the General Assembly, Amano echoed Ban’s tough approach, criticizing what he described as Iran’s lack of cooperation with the agency.

The New York conference is held every five years to review the Non-Proliferation Treaty, the pact aimed at stopping the spread of nuclear weapons. Technically, Iran is not on the agenda.

But the Obama administration sees the conference as a crucial opportunity to advance ideas to strengthen the fraying treaty, such as punishing nuclear cheaters and further regulating the supply of nuclear fuel.

IRAN AS THE ‘BIGGEST THREAT’

Iran is expected to block such steps. Any decision by the conference must be a consensus.

“This meeting is all about Iran,” said a White House official, speaking on the condition of anonymity because of diplomatic sensitivity. “Because Iran poses the biggest threat to the survival of the treaty.”

Clinton predicted Sunday that Ahmadinejad would try to divert attention from his nuclear program at a moment when an American-led drive to impose new economic sanctions is picking up steam.

Iran denies that it is building a bomb. But the IAEA censured Iran last year for secretly constructing a nuclear facility and defying U.N. resolutions on uranium enrichment.

On Monday, Amano said the agency remains unable to confirm that all of Iran’s nuclear material is being used for peaceful purposes “because Iran has not provided the necessary cooperation.”