The five major powers with nuclear arsenals -- the United States, Russia, China, Great Britain and France -- are all signatories of the Nuclear Non-Proliferation Treaty, which binds them to guarantees monitored by the International Atomic Energy Agency (IAEA).

India and Pakistan, which have both openly tested nuclear bombs, and Israel, which is thought by experts to have nuclear weapons as well, are not subject to IAEA inspections because they have not signed the treaty.

Analysts remain divided as to whether North Korea's efforts to develop nuclear weapons have yielded concrete results.

Iran claims that its nuclear program is entirely oriented towards generating energy and says it is willing to accept inspections, but the United States in particular has asserted that Iran is trying to buy time to build a bomb and has demanded that it give up all its uranium enrichment activities.

The United States would like the IAEA to refer the case of Iran's suspected nuclear weapons program to the UN Security Council for possible sanctions.

Benn Tennenbaum, an expert at the Federation of American Scientists, thinks that "it will take several years" for Iran to develop a bomb if they only have the gas centrifuge program that is known to be in place. Even if it is fairly-well monitored, he said, "they still have the ability to divert some material," in which case it would take "a few years" to gather enough high-grade uranium to make a bomb.

"If they have a separate program, they would probably do it very quickly," he added, noting that such a program would not be subject to inspection.

"The IAEA is not a judge of the Non-Proliferation Treaty," explained Mark Gwozdecky, an IAEA spokesman. "We monitor countries' activities -- if there are compliance issues, they are referred to the UN Security Council," he added.

In early 2003 Pyongyang informed the United Nations of its withdrawal from the treaty and expelled IAEA inspectors, leading the agency to send the case of North Korea to the Security Council.

South Korea has recently admitted that it carried out plutonium experiments banned by the treaty.

Lybia's case was also referred to the UN, but only to provide information since Tripoli renounced at the end of 2003 all its programs of weapons of mass destruction.

After the first Gulf War in 1991, the United Nations extended extraordinary powers to AIEA and UN inspectors (UNMOVIC) to monitor Iraq's weapons-related activities.

There have also been good surprises, Gwozdecky said.

After the fall of Ceausescu, Romania's new leaders alerted the United Nations to possibly suspect activities, while Argentina and Brazil both renounced any nuclear ambitions before signing the non-proliferation accord.

South Africa was described by the IAEA as a "model of cooperation" for its supervised nuclear disarmament at the end of apartheid in 1993-94.

Kazakhstan, Belorus and Ukraine all agreed to ban any stockpiling of nuclear weapons on their national territory following the breakup of the Soviet Union in 1991.

Experts also note that several highly-industrialized nations -- Germany and the Netherlands, for example -- have a sufficiently developed technological infrastructure to quickly development nuclear weapons if they so decided.

"I would be concerned about Japan," Tennenbaum said. "They have a very large nuclear reactor complex and have enormous stockpiles of spent fuel, more than enough to build many bombs," he added.

"But they certainly don't have the desire to build it right now."

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