By Paul Reynolds
World Affairs correspondent, BBC News website
The crisis over Iran's nuclear programme has reached a new level with the reporting of Iran to the Security Council.
Iran has reacted immediately. It said it would withdraw cooperation over snap inspections, threatened to resume all its enrichment activities and declared that a potential deal with Russia was off. That adds to the sense of confrontation.
(Update 5 February: Iran now says that it might talk again with the Russians after all, though whether it is really willing to negotiate remains to be seen.)
The significance of the Security Council move is twofold.
First, the council has the power to impose sanctions. There is therefore the potential for escalation.
Second, the Western powers have managed to get Russia and China alongside.
Iran insists it has no intention of building a nuclear bomb
This enables the West to say that this is an international issue - not another Western confrontation with an Islamic country.
However, neither of these two key players is yet on board in terms of agreeing to any measures against Iran and it is not even clear what the Security Council itself might do.
It will certainly do nothing until next month when the director general of the International Atomic Energy Agency (IAEA) Mohamed ElBaradei makes another report on Iran. That was the compromise agreed by the US, Russia, China, Britain, France, Germany and the EU High Representative at a meeting in London on 30 January.
A great deal depends on that report.
If Mr ElBaradei gives Iran good marks, then Russia and China, who have only reluctantly agreed to the issue being taken to the council at all, will block any suggestion of sanctions.
16 Feb, Moscow: Russia and Iran resume talks on Russia's proposed compromise
March, Vienna: IAEA to report on Iranian compliance; possible Security Council action to follow
If Iran is found wanting, the council might initially issue some kind of warning that Iran must implement all the IAEA's demands on inspections. Iran has been dragging its heels on some of these, especially access to people, places and papers though it has recently made some further moves to comply.
The latest accusation against Iran from IAEA sources is that it possesses a document that shows how to mould highly enriched uranium into a nuclear warhead. Iran has shown this to the IAEA.
The US and its allies say the document indicates Iran's interest in nuclear weapons but Iran counters that it was simply given the document, unasked for, by the renegade Pakistani nuclear scientist A Q Khan, from whom Iraq once secretly acquired enrichment technology.
The essential point of difference with Iran - whether it should develop its own nuclear fuel cycle - remains.
Nobody knows how to solve this. Iran stands by its right to make its own fuel under the terms of the nuclear Non-Proliferation Treaty (NPT). All the treaty requires is that the procedure is placed under IAEA inspection. Iran further says that it will not build a bomb and that its supreme religious leader has issued a fatwa to that end.
'Five years away'
But the West does not accept that Iran should be allowed that right, given that it hid an enrichment programme for 18 years and cannot therefore be trusted.
Russia and China appear to be in the middle somewhere, uneasy about Iran but unwilling to press the point too far. Both have commercial interests in Iran. Russia is completing the nuclear reactor that the Germans started under the Shah. China signed a long-term agreement to buy oil and gas from Iran not long ago.
At some stage of course, the question will arise as to whether this will move from diplomacy to military action - nobody knows what the tipping-point might be
But those interests do not mean that they want Iran to acquire nuclear weapons technology. Russia has offered to enrich fuel for Iran and talks continue on that with some people hoping for a solution along those lines. However Iran has now, for the moment at least, closed the door to that.
The best perhaps that diplomacy can do is delay. Indeed a senior British official with close knowledge of the process is now talking of all this going on for several years.
"Five years ago," he said, "we said that Iran was five years away from being able to make a nuclear weapon. Now we still say that. That is progress."
Mr ElBaradei himself has suggested that Iran freezes its work for 10 years.
Up till now, Iran has been reluctant to go ahead too fast. Its tactics have been characterised by strong rhetoric but tentative actions.
It has held back from abandoning all restraint. It knows that if it did, rougher waters would be ahead. Action by the Security Council could follow.
At some stage of course, the question will arise as to whether this will move from diplomacy to military action. Nobody knows what the tipping-point might be.
British officials say this is "not on the agenda and is not even being discussed".
But with the US and Israel both saying that Iran should not be allowed to develop a nuclear weapon, at some stage it might get onto someone's agenda.