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 has called for the U.S. to be removed from the International Atomic Energy Agency, in his opening speech at a nuclear disarmament conference in Tehran.

Mr. Ahmadinejad said Saturday countries that do not possess nuclear weapons should review the Nuclear Non-Proliferation Treaty, which aims to halt the spread of technologies that can be used to produce nuclear weapons. There was no immediate reaction from the U.S.

The Iranian government is hosting the two-day conference to counter the 47-nation nuclear security summit held earlier this week in Washington. Iran was not invited to the U.S. meeting.

The Iranian government said foreign ministers and other high-ranking officials from more than 60 countries were expected to attend the conference in Tehran.

The U.S. is pushing for a fourth round of United Nations sanctions over Iran's disputed nuclear program, but Iran insists the program is for peaceful, civilian purposes.

The Iranian government is hosting a nuclear conference Saturday and Sunday in Tehran, in counterpoint to the Washington summit this week to which it was not invited. The meeting comes as the U.S. pushes for a fourth set of sanctions over Tehran's disputed nuclear program, a drive that appears to be gaining momentum.

Looking ahead to the Tehran meeting, Iranian President Mahmoud Ahmadinejad insisted that his country is doing its best to work with world powers.

In an interview on state television, Mr. Ahmadinejad said "we are actually after cooperation and negotiation. We still are.” He added that Iran was willing to deal with a formula that protects Iran's rights, includes its independence, dignity and honor - and excludes the nuclear issue.

It's that kind of mixed message that frustrates so many. Iran insists its nuclear program is for peaceful, civilian purposes. But by refusing to comply with U.N. nuclear agency requests, it deepens suspicions that it seeks nuclear weapons.

Ezzedine Choukri Fishere, political science professor at the American University in Cairo, says the Iranian program is worrying for almost everyone, both in the region and in the international community.

“The fact that Iran insists on pursuing these features and refusing to reassure the international community and its neighbors,” Fishere said, “means that those who are worried about it enough to take action, will eventually take action."

The conference in Iran appears aimed at showing Tehran still has supporters. India is one nuclear power sending a representative, though at a far lower official level than at the Washington summit.

There are signs others are losing patience. China, which has been holding out against further U.N. sanctions, has agreed to be involved at least in the drafting of new measures. The veto-wielding nation depends on Iran for some ten percent of its oil, although in recent months has been looking at other Persian Gulf nations as possible suppliers.

Further complicating efforts of those wishing to support Iran are comments by authorities that leave many simply baffled.

Earlier in the week, a senior official at Iran's atomic energy agency declared the country would become a member of the "nuclear club" within a month. The term is commonly used to describe nations with nuclear weapons.

U.S. Defense Secretary Robert Gates was quick to dismiss the idea, saying he didn't believe it.

“I think most estimates that I've seen haven't changed since the last time we talked about it, which is, at least a year, maybe more," Gates said.

Political science professor Fishere argued both sides need to go beyond reacting to statements like that about the nuclear club, which he says could be aimed at a domestic audience or simply a matter of mistranslation. He urged the United States and Iran to sit down to direct dialogue about all the issues at stake. But he argues that the offer by President Barack Obama to reach out to Iran didn't go far enough.

"What the Obama administration did was incurring the political cost of calling for a dialogue with Iran, but without actually the benefit of engaging in that dialogue,” Fishere said.

He added that he hopes the administration will be bold enough to finally engage in face-to-face dialogue and put on the table the serious issues and the real issues it is worried about.

Fishere said the U.N. offer last year to enrich Iranian uranium abroad -an offer rejected by Iran - was a good start, arguing that broadening that dialogue will help bring Iran back from what he calls the "abyss" that it appears to be approaching.

World leaders are heading for Washington to discuss what Barack Obama has described as "the most immediate and extreme threat to global security" - the risk that terrorists could acquire a nuclear bomb. But how likely is this scenario?

A former investigator with the CIA and the US department of energy, Rolf Mowatt-Larssen, says there are three headlines that keep him awake at night:

• Pakistani 'loose nukes' in the hands of terrorists

• North Korea supplies terrorists with nuclear bombs

• Al-Qaeda launches nuclear attack

The good news is that he thinks "the odds are stacked against" terrorists acquiring a nuclear bomb.

But the low probability, he argues, has to be weighed against the awfulness of the consequences.

In today's unpredictable world, he writes in an article for the Bulletin of the Atomic Scientists, "a probability-based approach to managing risk" makes less sense than one "focused on mitigating threats in descending order of their possible consequences".

It's an argument that Barack Obama was making long before his election.

"Instead of taking aggressive steps to secure the world's most dangerous technology, [the US has] spent almost $1 trillion to occupy a country in the heart of the Middle East that no longer had any weapons of mass destruction," he said in a speech at Purdue University, Indiana, in July 2008.

Three months later, a commission set up by the US Congress warned that without decisive action it was "more likely than not" that a terrorist attack involving WMD would occur by the end of 2013.

Pakistan

In Rolf Mowatt-Larssen's view, there is "a greater possibility of a nuclear meltdown in Pakistan than anywhere else in the world".

The region has more violent extremists than any other, the country is unstable, and its arsenal of nuclear weapons is expanding.

Once a new plutonium reactor comes on line in the near future "smaller, more lethal plutonium bombs will be produced in greater numbers", he says.

The possibility of a Taliban takeover is, he admits, a "worst-case scenario".

But the Taliban and al-Qaeda are not the only shadows on the Pakistani landscape. There is also the Lashkar-e-Taiba militant group, which is accused of carrying out the Mumbai attack in November 2008, and like the Pakistani officer corps, recruits mostly in the Punjab.

"As one senior Pakistani general once told me," wrote Bruce Riedel of the Brookings Institution last week, "the relationship between the army and the Lashkar-e-Taiba is a family affair".

He went on: "Pakistan has taken serious measures to protect the crown jewels of its national security, but it lives in a perilous time. If there is a nightmare nuclear security scenario in Pakistan today it is probably an inside-the-family-job that ends up in a nuclear armageddon in India."

The point is echoed by Ian Kearns of the British American Security Information Council (Basic), who writes of the danger that states could use terrorist groups to attack adversaries "by proxy", engineering nuclear security breakdowns to facilitate terrorist access to weapons or materials.

BBC correspondents say there is every indication that the Pakistani military is in total control of the country's nuclear facilities.

North Korea

The reason North Korea keeps Rolf Mowatt-Larssen awake at night is connected with the mysterious site at al-Kibar in Syria, destroyed by Israeli missiles in 2007.

It's his view that North Korea was helping Syria build a reactor there and that the outside world only found out because of a "windfall of intelligence".

"Taking into account the sobering reality that Kim Jong-il came close to providing Syria with the building blocks for nuclear weapons... how confident can the international community be that there is not a long-running 'AQ Kim' network in North Korea that is analogous to the AQ Khan rogue state nuclear supplier network in Pakistan?" he asks.

The episode showed, in his view, that it is hard enough for the intelligence community to spot state-related clandestine nuclear activity, let alone clandestine nuclear trafficking of non-state actors, which would have a much smaller footprint.

North Korea's "erratic and irresponsible behaviour" makes it a leading potential source for terrorists seeking to acquire nuclear-related technologies and materials, he says.

Al-Qaeda

Though he now works in academia, Rolf Mowatt-Larssen led US efforts to determine whether al-Qaeda possessed a nuclear bomb, in the wake of 9/11.

He doesn't believe it does. But "the group's long-held intent and persistent efforts to acquire nuclear and biological weapons represent a unique means of potentially fulfilling their wildest hopes and aspirations," he writes.

Al-Qaeda's experience on the nuclear black market has taught its planners that its best chance lies in constructing an "improvised nuclear device (IND)," he says.

For this they would need either a quantity of plutonium or 25kg-50kg of highly enriched uranium (HEU), the size of one or two grapefruits.

HEU is held in hundreds of buildings in dozens of countries. "Security measures for many of these stocks are excellent, but security for others is appalling," according to a report published in 2008 by the Nuclear Threat Initiative.

The IAEA registered 15 confirmed cases of unauthorised possession of plutonium or HEU between 1993 and 2008, a few of which involved kilogram-sized quantities. In most cases the quantity was far lower but in some cases the sellers indicated there was more. (If there was, it hasn't been traced.)

There is no global inventory of either material, so no-one can be sure how much has gone missing over the years.

Neither are there agreed international standards for security and accounting of these materials. UN Security Council Resolution 1540 merely calls for "appropriate and effective" measures, without defining this in detail.

"It is a stark and worrying fact, therefore, that nuclear materials and weapons around the world are not as secure as they should be," writes Ian Kearns, in his Basic report.

The main goal of the Washington summit is to make progress on this issue.