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.