By Paul Reynolds
World affairs correspondent, BBC News website
UK Prime Minister Gordon Brown's renewed offer of cooperation with Iran over nuclear power is designed to back up the "extended hand" gesture from President Obama as Western governments desperately try to avoid a potentially dangerous future confrontation.
The idea is to entice Iran into giving up its own programme of enriching uranium to use as fuel in its future nuclear reactors, in exchange for a guaranteed supply of fuel from outside and for other economic incentives and political contacts.
Mr Brown has proposed a reduction in the UK's nuclear warheads.
The problem is that most of this has been on the table for some time and has not been picked up.
The new element, the proposal for direct contacts by the new US administration, is of uncertain value at this stage. But Western countries feel they have to try.
And if Iran does not cooperate, what then? All is unclear. Mr Brown's threat of more sanctions was not accompanied by any evidence that Russia or China would agree, and without them the Security Council cannot act. Sanctions imposed so far might have slowed down the enrichment but has certainly not stopped it.
It is difficult to see why Iran should now agree to change a policy that has confused its opponents and has enabled it to reach a level of technological achievement that cannot be undone.
Nobody yet knows whether the Obama administration will conclude that a military strike on Iran would cause more harm than good.
It does not yet at least take such an apocalyptic view as Israel. The Israeli Chief of Staff Gabi Ashkenazi has told the Americans that, while diplomacy should come first, military action might have to come second. The likely next Israeli prime minister, Benjamin Netanyahu, does not disagree.
But there is an Iranian presidential election coming up in June (from which one of the moderate candidates, former President Khatami, has withdrawn) and the current Iranian President Mahmoud Ahmadinejad is likely to run.
So it is difficult to see why Iran should now agree to change a policy that has confused its opponents and has enabled it to reach a level of technological achievement that cannot be undone.
There was no hint in Mr Brown's speech that the US or the EU might accept a limited Iranian programme of enrichment under international inspection, which might be a middle way forward.
Elsewhere in his speech, which was about nuclear proliferation in general as well, the UK leader also proposed to further reduce Britain's own nuclear warheads in the run-up to the next five-yearly proliferation review conference next year. These warheads now number fewer than 160.
The weakness in his argument, other governments might say, is that at the same time Britain is also starting on a major programme of renewing its nuclear weapons.
Western governments want Iran to get all its nuclear fuel from outside
It is planning to build four new submarines, will take part in an American programme to extend the life of the Trident D5 missile and is examining an upgrade for its own warheads.
Mr Brown put forward some ideas for strengthening the Nuclear Non-Proliferation Treaty, under which non-nuclear-armed states using nuclear power agree not to develop nuclear weapons. Leaving the NPT should in future lead to automatic sanctions, he suggested.
This would be an effort to stop a loophole (renouncing the treaty) that North Korea has already used and Iran could do one day, especially if attacked.