Iranian President Mahmoud Ahmadinejad says a nuclear fuel swap deal Tehran recently reached with Brazil and Turkey is the "last opportunity" to resolve a long-standing nuclear dispute between Iran and the West.

President Ahmadinejad presented his argument with characteristic oratorical verve, saying a nuclear fuel swap deal worked out by Brazil and Turkey last week was a "final opportunity" that must not be lost by the international community.

He says that President Barack Obama should understand that this agreement is a historic chance to show that he wants to create change, to respect the rights of other nations, and to give up what he calls the erroneous policies of past American administrations.

He also appealed directly to President Obama to use his influence to better what he called the "political future of the world" and to oppose those whom he says are counseling Mr. Obama to take a tough stance against Iran.

The United States and other top Western powers have been critical of the recent fuel-swap deal, arguing it does nothing to allay fears that Iran is trying to build nuclear weapons. A similar deal was first proposed last October, when Tehran had a much smaller stockpile of enriched uranium.

Mr. Ahmadinejad also criticized Russia for siding with the United States on a plan to impose a fourth round of U.N. sanctions on Iran. The proposal is being debated in the U.N. Security Council. The resolution appears to have the backing of the Security Council's five veto-wielding permanent members, including China and Russia.

Editor Alex Vatanka of Janes' Islamic Affairs Analyst argues the three main centers of power in Iran, President Ahmadinejad, Ayatollah Ali Khamenei, and the powerful Revolutionary Guard Corps, have conflicting views about the nuclear deal.

"I think it is quite complex, because, whereas the IRGC and the Supreme Leader might have their own survival at stake, Ahmadinejad sees himself differently. He sees himself as the elected official who has to go for the popular vote," Vatanka said. "And he knows that overhauling relations with the United States could really generate some good will in Iran, because, by and large, despite what everyone in the world thinks, there is a lot of pro-American sentiment in Iran. And a lot of people in Iran appreciate that one of the biggest obstacles in improving their lives is the international isolation that they are facing, and that America is crucial in keeping Iran isolated."

Vatanka also believes Iranian Supreme Leader, Ali Khamenei, is not in a strong position to oppose Mr. Ahmadinejad, should he attempt a rapprochement with the United States, and the Revolutionary Guard, while powerful, remains divided among itself.

Iranian President Mahmoud Ahmadinejad kicked off the Nuclear Non-Proliferation Treaty (NPT) Review Conference with a lengthy diatribe against the United States and other Western powers who seek to sanction his country for its controversial nuclear program.

Mr. Ahmadinejad spoke for more than half an hour, giving what has become something of his trademark - a speech criticizing the United States, Israel and invoking God - and sending the U.S., British and French delegations walking out of the hall in protest.

He said the possession of nuclear bombs is not a source of pride, but is "disgusting and shameful."

"And even more shameful is the threat to use or to use such weapons, which is not even comparable to any crime committed throughout history," said President Ahmadinejad.

He criticized the United States for being the first nation to produce and use a nuclear bomb during World War II, saying it is one of the most hated countries in history.

And he accused Israel, which is widely believed to possess nuclear weapons but denies it, of stockpiling hundreds of nuclear warheads and receiving assistance for its nuclear program from the United States and its allies.

But despite his anti-nuclear weapons rhetoric, it is Mr. Ahmadinejad's government that is under a cloud of international suspicion for what many states believe is a covert program to produce atomic weapons. A possible fourth round of sanctions against Iran for failing to stop enriching uranium is being negotiated among major powers at the United Nations.

U.N. Secretary-General Ban Ki-moon encouraged President Ahmadinejad to "engage constructively" and comply fully with existing U.N. Security Council resolutions and cooperate with the International Atomic Energy Agency.

"Let us be clear: the onus is on Iran to clarify the doubts and concerns about its program," said Ban Ki-moon.

He urged the Islamic Republic to accept a nuclear fuel supply proposal from the IAEA that has been on the table for many months, saying that would be an important confidence-building measure.

Mr. Ahmadinejad replied to Mr. Ban in his opening remarks, saying Iran had accepted the fuel exchange deal.

"Well I would like to tell you and inform him as well, that we accepted that from the start," he said. "And I would like to announce that for us 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."

But in fact, Iran has not sent any firm reply to the international community and has sought to change the terms of the original proposal.

Later Monday, U.S. Secretary of State Hillary Clinton will address the review conference.

Conferences to review the operation of the NPT have been held every five years since the treaty went into effect in 1970, becoming the main legal barrier to the spread of nuclear arms. Delegates from the 189 countries belonging to the treaty will discuss compliance with its three pillars - nuclear disarmament, nuclear non-proliferation and peaceful uses of nuclear energy.

The month-long review conference will also likely focus on Iran's non-compliance with U.N. Security Council resolutions and IAEA safeguards, North Korea's withdrawal from the treaty in 2003 and its subsequent two nuclear tests, and the possible implementation of a 1995 resolution on establishing a nuclear-weapons-free zone in the Middle East.

The White House said Monday that Iranian President Mahmoud Ahmadinejad's harsh criticisms of the United States, other Western powers, and Israel at a conference reviewing the Nuclear Non-Proliferation Treaty, or NPT, demonstrate Tehran's increasing isolation as it faces international pressure over its own nuclear ambitions.

At a White House press briefing, Spokesman Robert Gibbs called the Iranian president's remarks "predictable" in that the Tehran government continues to fail to speak about nonproliferation obligations that itself refuses to live up to.

American, British and French officials "rightly" walked out, said Gibbs, as the Iranian leader make a series of "wild accusations."

"Those that are involved in the NPT conference, that are living up to the obligations, would have wanted to hear the Iranians discuss living up to their obligations," said Robert Gibbs. "I think them not doing that again shows how further isolated they are from the world community. And we continue to make progress on sanctions at a multilateral level, even as we look at ways that we can do so within our own government."

The United States, Gibbs said, continues to work with other U.N. Security Council members, moving forward on developing a new sanctions resolution, but he offered no new details on this process.

At the end of a nuclear security summit he hosted in Washington last month, President Barack Obama said he knew negotiations could be difficult, but that he would push as hard as he could to ensure that a resolution contains strong sanctions with "consequences for Iran."

In his address at the NPT conference, the Iranian leader attacked the United States and Israel, saying the production, stockpiling of nuclear weapons or threats to use them is "for people characterized by a lack of consistent logic and behavior."

Responding to President Ahmadinejad, U.S. Secretary of State Hillary Clinton told the nonproliferation conference in New York that Iran has defied the U.N. Security Council and the International Atomic Energy Agency and placed the Nonproliferation Treaty in jeopardy.

Against the background of the Iranian president's attacks on Israel at the New York conference that the White House made a point on Monday of reiterating the strong U.S. commitment to Israel's security.

White House Press Secretary Gibbs told reporters that President Obama, during a 20 minute telephone conversation with Israeli Prime Minister Benjamin Netanyahu, reaffirmed his "unshakeable" commitment to Israel's security.

Iranian President Mahmoud Ahmadinejad is on his way to New York City to take part in a conference on the Nuclear Non-Proliferation Treaty.

Mr. Ahmadinejad is due to address delegates Monday on the first day of the month-long conference at U.N. headquarters. He is expected to defend Iran's right to enrich uranium, and to propose changes to the treaty.

Before leaving Tehran for New York, Mr. Ahmadinejad criticized the production and stockpiling of nuclear weapons.

Iran is a signatory to the Nuclear Non-Proliferation Treaty, which is designed to check the spread of atomic weapons worldwide.

However, the United States accuses Iran of secretly working to produce a nuclear weapon. The U.S. and its allies are seeking a fourth set of U.N. sanctions to pressure Iran to stop enriching uranium.

Iran says its enrichment program is for peaceful purposes.

U.S. Secretary of State Hillary Clinton is also scheduled to address the conference on Monday.

The review conference of states that are party to the Nuclear Non-Proliferation Treaty has been held every five years since the treaty went into effect in 1970.

An Israeli official says an Iranian academic with ties to Iran's nuclear program has requested asylum in Israel. Israeli Deputy Minister Ayoub Kara said Saturday the Iranian academic is awaiting a decision on the asylum request in a country "friendly" to Israel. Kara did not identify the academic or the country. He said Israel will do all it can to help people who want to remove what he called the strategic and nuclear threat posed by Iran. Israel, the United States and other Western nations accuse Iran of trying to develop nuclear weapons. Iran says its nuclear program is peaceful. The Washington Post quotes U.S. officials as saying a growing number of Iranian nuclear experts are defecting or leaking information to the West about Iran's nuclear program. In a report published Sunday, the newspaper quotes current and former officials in the United States and Europe as saying some of the most significant new material has come from scientists and others with access to Iran's military programs. The Washington Post says U.S. officials have acknowledged that Iranian nuclear physicist Shahram Amiri defected to the West after disappearing on a pilgrimage to Saudi Arabia last June. Israel says a nuclear-armed Iran would be a threat to its existence because Iranian leaders have called for Israel's destruction. Israel is widely believed to be the only nuclear-armed nation in the region, but it refuses to confirm or deny possession of a nuclear arsenal. Former Israeli nuclear technician Mordechai Vanunu appealed to President Barack Obama to set him free from an Israeli jail since he wants to rid the world of nuclear weapons. The nuclear whistleblower has completed his full 18-year prison sentence for leaking classified information about Israel's nuclear capacity to the London-based Sunday Times in 1986. Israel still bans Vanunu from speaking to the foreign press and others as a condition for his release from jail.