Opening the month-long conference, UN Secretary General Kofi Annan said the Non-Proliferation Treaty (NPT) that limits the spread of nuclear weapons is out of date in the face of new threats and technology.

“The plain fact is that the regime has not kept pace with the march of technology and globalisation, and developments of many kinds in recent years have placed it under great stress,” Mr Annan said.

The NPT, signed in 1970, faces a new era of “rogue” states with alleged nuclear weapons programs, international nuclear smuggling rings and trans-national terrorist groups seeking weapons of mass destruction, he said.

Uncovered in the past two years was an international black market in technology that could be used to make atomic weapons, run by the ‘father’ of Pakistan’s atomic bomb, Abdul Qadeer Khan.

In December 2002 North Korea expelled inspectors from the International Atomic Energy Agency (IAEA), the UN’s nuclear watchdog, withdrew from the NPT, and now claims to have made atom bombs.

Mr Annan said the 188 nations meeting “must strengthen confidence in the integrity of the treaty, particularly in the face of the first withdrawal announced by a state.”

He also said the Vienna-based IAEA should be given more authority to inspect the nuclear programs of states that are party to the NPT.

Mr Annan singled out Iran, saying the NPT will not be sustainable if states develop “the most sensitive phases of the fuel cycle and are equipped with the technology to produce nuclear weapons on short notice.”

The US claims the Islamic republic is secretly developing atomic weapons under the cover of a civilian nuclear power program that is under IAEA safeguards.

UN nuclear chief Mohamed ElBaradei made a plea for Iran and the European Union to keep their nuclear talks alive and for Tehran to refrain from uranium enrichment.

Iran has said it is unhappy with the progress of the negotiations and may resume uranium conversion activities in defiance of the agreed suspension.

The UN chief also said those countries permitted to possess nuclear weapons – the US, China, Russia, Britain and France – must move forward on disarming.

“An important step would be for former Cold War rivals to commit themselves, irreversibly, to further cuts in their arsenals so that warheads number in the hundreds and not the thousands,” he said.

Three states that have not signed the NPT but are understood to have nuclear arms are India and Pakistan, which have both announced missiles tests in the past, and Israel, which denies possessing any nuclear weapons.