After months of deadlock, suddenly the diplomatic confrontation over Iran's nuclear programme has burst back into life.
On Monday, Iran signed a deal with Brazil and Turkey, under which a large part of Iran's stocks of enriched uranium would be shipped to Turkey in exchange for new fuel for a Tehran research reactor.
It was widely seen as a last-ditch effort by President Mahmoud Ahmadinejad to deflect pressure for fresh sanctions, a diplomatic coup possibly enabling him to slip out of the encircling net.
But despite that, on Tuesday US Secretary of State Hillary Clinton announced agreement among the permanent five members of the security council on a new draft UN Security Council resolution on sanctions.
It is not clear whether the 10 non-permanent members of the council will support the draft. They include Brazil and Turkey, who have both said new sanctions are not now necessary.
But Mrs Clinton's comments strongly suggest that the hard-won support of China and Russia for the sanctions has withstood the blandishments of Mr Ahmadinejad.
At the same time Turkish Prime Minister Recep Tayyip Erdogan, while calling on the world to give the deal a chance, warned Iran that if it did not deliver the fuel in one month, as agreed, it would be "on its own".
Iran watchers are already criticising Washington for moving the goal posts.
The state department spokesman seemed to suggest that only the suspension of uranium enrichment by Iran would be enough to stop the new sanctions.
A senior US official said the negotiations on a fuel swap were on a "separate track" from the discussions over sanctions - and the deal with Brazil and Turkey, while well intentioned, was "largely beside the point".
Turkey and Brazil may also feel disappointed that this rapid announcement by the US secretary of state undermines their effort to find a diplomatic solution.
The problem for the United States and its allies is that they are very keen to keep the pressure on Iran.
Any suggestion that they are willing to hold off on sanctions and the coalition, so tortuously assembled, might begin to fall apart.
The West would fear that it might also give Iran the option to play for time.
After all, they might argue, this latest deal was only won under threat of those very sanctions.
The deal itself certainly leaves plenty of unanswered questions. The Institute for Science and International Security (ISIS), a Washington think tank, pointed to one of the most obvious.
What happens to Iran's enriched uranium, shipped to Turkey, if and when it gets the fuel for its research reactor?
Under the original deal negotiated in Geneva last October, it was that low-enriched uranium that would be converted to higher-grade fuel for the Tehran research reactor.
Under this deal, it just sits in Turkey, while France provides fresh fuel for the research reactor.
Nothing in the agreement stipulates whether or not Iran gets its low-enriched uranium back.
Another point made by the ISIS is that the situation has changed since the original deal in October.
At that time, 1,200kgs of uranium made up the bulk of Iran's stocks.
Shipping it out of the country provided a high measure of security that it could not be diverted to make a bomb.
But since then Iran has been busily enriching. It may now possess more than 2,000kgs of enriched uranium.
And what happens also to the higher grade uranium - 20% grade - that Iran says it has been producing itself for the Tehran reactor?
A more fundamental question is whether President Ahmadinejad can actually deliver on this deal.
Two previous attempts to reach a similar agreement fell apart, when Mr Ahmadinejad came under sustained criticism at home.
It was the clearest evidence of the weakening of his domestic political position following last summer's election dispute.
This time, reaction in hardline newspapers has been less negative but still mixed.
Jomhuri-e-Eslami, which is seen as a hardline supporter of the supreme leader, Ayatollah Khamenei, said the deal was "an obvious backtrack from Iran's announced strategy.
It said: "This declaration is not a victory for Iran but it is an obvious backtrack against the bullying demands of the West and the Islamic Republic of Iran should not accept it."
By contrast Keyhan, also seen as close to the supreme leader, said Iran had not backtracked, but rather "gained the objective guarantee that it was seeking".
So even hardliners in Iran are divided. One can only imagine how much greater those divisions are likely to become if they see that the moment is approaching for Iran's hard-won uranium to be sent out of the country, particularly if sanctions are still on track.
Perhaps Mr Ahmadinejad himself is bluffing, reaching a deal he believes he will never actually have to implement.
In that case, Washington might decide the best course is to call his bluff and agree to the deal.
Meanwhile in New York, US officials are confident they have the votes they need for new sanctions - in other words, they have the support of nine members of the security council, and no vetoes from the permanent members.
But Western officials have always stressed the need for as much support as possible, so as to send the strongest possible message to Tehran.
Abstentions or negative votes from powerful countries such as Turkey or Brazil would be very damaging.
Another issue is the timing.
It has always been assumed that no vote would come forward this month while Lebanon is chairing the Security Council, because of the influential role of Iran's Hezbollah allies in Lebanon.
If it does slip to June, then the Americans have to decide whether they feel a vote would be productive in the sensitive days running up to the first anniversary of Mr Ahmadinejad's re-election on 12 June.
So a deal, originally put forward as a confidence-building measure, risks just becoming a new source of bitter debate between Iran and the West.