AHMADINEJAD TO ATTEND UN NUCLEAR TALKS IN NEW YORK
Iran has denied it intends to make a nuclear weapon
Delegates from nearly 200 nations were gathering at the UN to review efforts to check the spread of nuclear weapons.
They meet every five years to try to strengthen the nuclear non-proliferation treaty.
But this time the unresolved Iranian nuclear crisis threatens to overshadow the conference in New York.
Iran's President Mahmoud Ahmadinejad made a last-minute decision to attend to defend his country against US claims it wants to build a bomb.
The nuclear non-proliferation treaty, or NPT, is a grand bargain: nations with nuclear weapons promise to disarm, while those without promise not to get them, in exchange for the right to peaceful use of nuclear energy.
But the regime has come under heavy strain in recent years, and veteran observers say Monday's conference cannot afford to fail.
Participants say a positive atmosphere has been created by the commitment of US president Barack Obama to tackle nuclear issues.
However, America is leading the charge to strengthen NPT measures against countries such as Iran, which it accuses of secretly trying to build a bomb.
That is something Iran strongly denies, and President Ahmadinejad is attending in person to make his case.
Some diplomats fear the controversy will prevent a successful outcome of the conference.