Leading article: Visions of a safer world

When Barack Obama was awarded the Nobel Peace Prize last autumn, there was much criticism, and not just from the US President's opponents, to the effect that the prize had been given for promise rather than achievement. Six months on, the committee's choice is starting to look less wishful than it did.

Last week, Mr Obama signed the first new nuclear arms treaty with Russia for 30 years. He also announced a review of the US nuclear posture. And yesterday he welcomed to Washington delegates from 47 countries – most of them heads of state or government – to consider nuclear security worldwide. It is the largest gathering of states in the US since the 1940s.

There may be many reasons why Mr Obama has called this gathering now, beyond the most obvious one: the risk of nuclear material and even weapons getting into the wrong hands. The first and most obvious is the challenge posed by Iran. The precise nature of Tehran's nuclear intentions is still unclear. What is clear, however – whether because the leadership is divided or because it is deliberately trying to conceal its activities – is that Iran has not come clean with the International Atomic Energy Agency.

The US will want to send Iran an unambiguous warning of the risks of failing to cooperate – a message that will be effective only if it comes with broad support. Mr Obama needs such clarity for domestic political purposes, too. But he also needs an accurate gauge of the appetite for sanctions. They must not reinforce the divisions opened by the Iraq war.

North Korea and the Indian Subcontinent are other areas of concern, along with terrorism. The nuclear agreement the US concluded with India was unwelcome in Pakistan, where security of nuclear materials and expertise remains an issue, as it does with North Korea. And despite the recent US-Russia agreement, the reluctance of existing nuclear powers to reduce, or give up, their stockpiles remains a source of friction with many non-nuclear countries.

When the meeting ends today, the prospects for agreeing global guidelines on nuclear security should be clearer. But the main merit of this top-level gathering is that it happened at all.