By Paul Reynolds
World Affairs correspondent, BBC News website
Despite a shift in policy which has brought Washington closer to the European negotiations over Iran's nuclear programme, the talks are still in trouble.
A deal? Iran negotiator Hassan Rowhani and German Foreign Minister Joschka Fischer
The American move to offer Iran incentives and a European threat to take Iran to the Security Council have opened up a window for a new more combined approach which had been lacking before.
But the fundamental issue remains the same. Will Iran will give up its intention of developing a uranium enrichment process?
Iran is threatening to set a deadline in the talks, the Europeans are about to make an assessment of the progress, or lack of it, so far,
but the potential crisis will not be reached until later this year, according to a Western expert who has just been to Iran.
Dr Gary Samore of the International Institute for Strategic Studies in London said: "It is very likely that Iran will avoid a breakdown in the talks until after presidential elections in June and the formation of a new cabinet in September. The crunch point will probably not be until the fall."
Dr Samore said that all Iranian officials he had met rejected both publicly and privately the permanent cessation of uranium enrichment, the central issue in the talks with the so called European Three - Britain, France and Germany.
"At the same time," he went on, "Iran is reluctant to pick a fight with the Security Council. It is feeling somewhat isolated. The US and EU have made up on this, its ally Syria is under pressure in Lebanon and the Palestinians and Israelis are talking.
"The United States has been very smart in changing its position. It has made a deal with the Europeans over carrots and sticks for Iran. This makes it more likely that the talks will continue and more likely that the Europeans will blame Iran if there is a breakdown.
"I told the Iranians that the Americans had crossed a psychological threshold. Iran has always said it is the US which counts. Now Iran has the chance of naming a price for stopping enrichment. I do not know, though, if it will do so."
The fact that Dr Samore, who worked on nuclear non- proliferation in the Clinton administration, was granted a visa is being seen as part of an effort by Iran to persuade the outside world that its nuclear ambitions are peaceful.
But the talks are no nearer a result.
A letter on 10 March to the EU from the European Three stated that "while progress is not as fast as we would wish, we believe we are moving in the right direction".
This is diplomatic jargon for: "Some minor issues are OK but the big deal is a long way off."
The big deal, from the European and American point of view, would be an agreement by Iran not to enrich uranium as fuel for its nuclear power programme.
The West sees the acquisition by Iran of enrichment technology as dangerous in itself - because the same process which enriches uranium to the level needed for nuclear fuel can also be used to enrich to the higher level needed for a nuclear bomb.
And the West fears that Iran might use this technology to build a bomb either secretly, or legally by leaving the Nuclear Non-proliferation Treaty (NPT) and doing so anyway.
If it agrees to abandon enrichment, Iran would get a bagful of goodies, including assured fuel for its nuclear reactors from outside suppliers, support for its membership of the World Trade Organisation and easier trading conditions.
If it refuses, it could be reported to the Security Council. That might result in a demand for it not to enrich and sanctions if it does.
The talks are stalled on what is meant by "objective guarantees" that Iran will not build a nuclear bomb.
Each side interprets "objective guarantees" in a completely different way.
Only by giving up enrichment entirely, the West believes, could Iran provide such "objective guarantees" especially in view of its past violations of the Nuclear Non-proliferation Treaty. It hid an enrichment programme for 18 years.
From the Iranian point of view, the big deal would be for the rest of the world to accept that the "objective guarantees" would take the form of intrusive inspections by the UN nuclear agency the International Atomic Energy Agency (IAEA).
It would then be allowed to enrich quite legally.
Such inspections, it says, would take care of fears about a secret programme. It also says that it needs to be able to make fuel to ensure its security of supply and that it is allowed to do so under the NPT.
So defining "objective guarantees" is rather difficult.
So far it has proved impossible.
And even now, there are reports that Israel is preparing a military strike against Iranian nuclear installations if the talks fail.
The London Sunday Times says that secret plans for a combined air and ground assault have been drawn up.
However, the Israelis have not given up on the diplomatic track yet and retired general Ephraim Sneh, a member of the Knesset's Foreign Affairs and Defence Committee, says that military action would be used only as a last resort.
That also means, of course, that it is an option at some stage.