Delegates from 189 countries today are opening a new bid at the United Nations to prevent the spread of nuclear weapons, at a contentious meeting set to be dominated by Iran's presumed efforts to build a bomb, and fierce argument over the undeclared nuclear arsenal of Israel.
The month-long review conference of the Nuclear Non-Proliferation Treaty (NPT), generally considered the most important international arms-control agreement, takes place every five years. But it has produced few breakthroughs since it came into force in 1970: indeed the last one in 2005 failed to even come up with an agreed final statement.
This time the omens are little brighter, while the deepening crisis over Iran's uranium-enrichment programme means the stakes are especially high, and magnified further by the presence of Mahmoud Ahmadinejad. The Iranian President, the only head of state attending, is due to address the gathering at its opening session today, ahead of Hillary Clinton, the Secretary of State.
Yesterday senior US officials were playing down the chances of a deal. Washington's goal is rather to build the broadest possible coalition against Iran, to strengthen its hand in securing tough sanctions against Tehran.
Unlike Israel, India, Pakistan and North Korea, the recent additions to the nuclear club, Iran is a signatory of the NPT – a treaty that amounts to a grand bargain committing adherents not to seek nuclear weapons, in return for a pledge from the five traditional nuclear powers to move to eliminate their own arsenals.
Tehran continues to insist that its programme is purely peaceful in intent, despite growing evidence to the contrary. Yesterday Ms Clinton again accused Iran of being in breach of its obligations, and described Mr Ahmadinejad's trip to New York as a stunt aimed at confusing the issue and diverting global attention from his country's treaty violation.
As a signatory, Iran can – and certainly will – block any agreed statement not to its liking that would seek to tighten non-proliferation rules and authorise more intrusive inspections by the IAEA, the UN's atomic watchdog agency. Success for Washington will be measured by its ability to limit Iran's support to its few habitual allies of Cuba, Syria, and Venezuela and on occasion Libya, and to win agreement to punish countries that pull out of the NPT, as North Korea did in 2003.
In contrast to the last review – held at a time when President George W Bush did not hide his disdain for multilateral negotiations – the Obama administration comes into the conference with relatively shining credentials.
It has just signed an arms-reduction deal with Russia that slashes by a third the deployed strategic arsenals of the two countries, which hold over 90 per cent of the world's nuclear weapons. Mr Obama himself has set out a vision of a nuclear-free world, and last month hosted the biggest international conference on US soil since 1945, aimed at keeping nuclear materials out of terrorist hands.
But the US will come under renewed pressure finally to ratify the 1996 Comprehensive Test Ban Treaty. Mr Obama has called for Senate ratification, but faces opposition likely to be strengthened by Republican gains at November's mid-term elections here.
The other big complication, though is Israel. Israel's Prime Minister Benjamin Netanyahu abruptly pulled out of the nuclear security summit in Washington for fear the occasion would be turned into a debating forum on his country's arsenal, but the issue will surface again at the NPT conference.
Frustrated in Washington, Egypt is set to repeat its demand for a nuclear-free zone in the Middle East – a proposal that would both force the Israelis to give up their stockpile, and oblige Iran to abandon its quest for a nuclear weapon.