The Nuclear Non-Proliferation Treaty or NPT, which celebrates its 40th birthday this week, may have succeeded in keeping the number countries in possession of nuclear weapons down to a mere handful.

But the treaty, drawn up during the Cold War period, is now in urgent need of an overhaul if it is to meet present-day challenges such as the proliferation crises in North Korea, Iran and most recently Syria, experts said.

Furthermore, the United States should take the lead in bolstering the legitimacy of the NPT and the entire non-proliferation regime by dismantling its nuclear arsenal, the experts said.

Opened for signature on July 1, 1968 and put into effect on March 5, 1970, the NPT is the most universal arms control treaty in force.

Its stated goal is to stop the nuclear arms race and seek nuclear disarmament.

Five countries that had tested nuclear weapons before the treaty's completion -- China, France, Russia, Britain and the United States -- were recognised as nuclear-weapon states and obligated to pursue "effective measures" toward nuclear disarmament.

All others were designated non-nuclear-weapon states and prohibited from acquiring nuclear arms at all.

A major problem was that no specific target date was laid down for disarmament.

And with the nuclear states apparently reluctant to dismantle and destroy their nuclear arsenals, the non-nuclear weapon states see little incentive to keep their part of the bargain.

It had created a world of "nuclear haves and have-nots ... which cannot be sustained indefinitely," said Daryl Kimball, executive director of the Arms Control Association in Washington.

"Nuclear weapons are dangerous no matter who possesses them," he told AFP.

K. Subrahmanyam, a former director of the Indian Institute for Defence Studies, agreed.

"It cannot be legal for some countries to possess a category of weapons while it is illegal for others to do so. A regime that is based on such inequity cannot be expected to be stable or secure against further proliferation," Subrahmanyam wrote in a recent article for the Arms Control Association.

Perhaps one of the NPT's biggest flaws is the limited power there is to enforce it.

Inspections, carried out by the International Atomic Energy Agency in Vienna, are voluntary and countries largely control inspectors' movements.

Furthermore, there are no penalties for breaking the NPT, apart from being reported to the UN Security Council.

Experts acknowledge the NPT's success in curbing the number of states in possession of nuclear weapons.

"In 1960, (US President) John F. Kennedy warned as many as 20 nations could acquire a nuclear weapon in less that decade. They didn't," said Joe Cirincione, President of the Washington-based Ploughshares Fund.

"There are only nine countries with nuclear weapons today. Why? A big part of the reason is the bipartisan, multinational effort that lead to the NPT," Cirincione told AFP.

Thanks to the NPT, "there are now far fewer countries that have nuclear weapons or weapon programmes than there were in the 1960s, 1970s or 1980s," the expert said.

Nevertheless, the non-proliferation regime had suffered important setbacks, notably the cases of North Korea and Iran, and more recently Syria.

North Korea developed an illicit nuclear weapons programme, which it is only now in the long and slow process of dismantling.

Iran is accused of pursuing a weapons programme under the guise of peaceful nuclear power and Syria has recently come under fire for allegedly building a covert nuclear facility.

"These recent setbacks are not the fault of the NPT structure, but rather a problem of enforcement and international support," said Cirincione.

"Too often 'realpolitik' will influence decisions like the Indian Nuclear Deal that undermine the treaty. The NPT is very clear. All proliferation is bad, not just proliferation among potential enemies."

Kimball similarly believes the United States is undermining the NPT, not only by repudiating its disarmament commitments, but by seeking to carve out special exemptions from the rules for allies such India.

It was therefore up to the United States to take the lead if the NPT is going to survive, the experts said.

"Most of the 183 non-nuclear nations that have signed the NPT believe what the treaty says: No one should have nuclear weapons. It is time for the United States to mean it, too," said Cirincione.

"The NPT is not doomed to failure," said Kimball.

"But in order to survive well into this century, states must renew, strengthen, and fulfill the NPT bargain -- and soon."