The five major nuclear powers - the US, the former Soviet Union, China, the UK and France - agreed eventually to disarm. Other signatories agreed never to develop nuclear weapons in return for receiving full access to civilian nuclear technology.
But, our correspondent says, this grand bargain is looking increasingly threadbare, with critics arguing that the original nuclear weapons states have not taken their disarmament responsibilities seriously.
North Korea has walked away from the NPT to develop its own nuclear deterrent, while Iran is thought by many to be going as far as it can towards a nuclear weapons capability whilst remaining inside the treaty, he adds.
Two nuclear weapons states - India and Pakistan - along with Israel, which has an unacknowledged nuclear arsenal, are not signatories.
Iran says it is increasing uranium enrichment from 3.5% needed for commercial nuclear reactors
Iran says it has started enriching to 20%, needed for a medical research reactor near Tehran
Weapons-grade uranium is at least 90% enriched
Experts say achieving 20% is a key step towards weapons grade
In his speech on the opening day of the month-long NPT review conference at UN headquarters in New York, Iran's president insisted there was no "single credible proof" that it was breaching the agreement.
Mr Ahmadinejad criticised nuclear powers for failing to disarm, saying their "production, stockpiling and qualitative improvement of nuclear armaments... now serves as a justification for the others to develop their own".
"The nuclear bomb is a fire against humanity, rather than a weapon of defence. The possession of nuclear bombs is not a source of pride. Its possession is disgusting and shameful," he said.
He then attacked the US for refusing to rule out the use of nuclear weapons against other countries, including Iran.
NPT members should consider "any threat to use nuclear weapons or attack against peaceful nuclear facilities as a breach of international peace and security", and punish aggressors with suspension from the board of the International Atomic Energy Agency, he added.
A White House spokesman later dismissed the "wild accusations".
Earlier, the UN's secretary general urged nuclear weapons states to reaffirm their "unequivocal undertaking to eliminate nuclear weapons".
"Failure to do so would be a step backward," Mr Ban said.
He also called on Iran to "fully comply" with the UN resolutions on its nuclear programme and to co-operate with IAEA inspectors.
"The onus is on Iran to clarify the doubts and concerns about its programme," he said.
Libran Cabactulan, the Philippine diplomat presiding over this year's NPT review, has said the main aim of many signatories was to press nuclear powers to move more rapidly toward disarmament.
The Non-Aligned Movement has submitted to a detailed "plan of action" for moving towards global nuclear disarmament by 2030. It includes full ratification of the 1996 Comprehensive Test Ban Treaty.
Participants say they have been encouraged by US President Barack Obama's commitment to tackle nuclear issues.
He has spoken of his aspiration for a nuclear weapons-free world and recently signed a major arms reduction treaty with Russia.
He has also pledged to push for US ratification of the CTBT, which was rejected by the Senate in 1999.
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