By Jonathan Marcus
BBC News diplomatic correspondent
French Foreign Minister Bernard Kouchner has again raised the spectre of a conflict with Tehran, warning the world "to prepare for the worst... and the worst means war".
This is one of the strongest indications yet of the new Atlanticist accent to French foreign policy under the new President Nicolas Sarkozy.
Iran's nuclear programme remained secret for years
The hardening of France's position towards Tehran was first signalled by the new president in a speech to French ambassadors last month.
Then he called for tougher economic sanctions against Tehran and warned that if these failed to halt Iran's nuclear programme, there would be, as he put it "a catastrophic choice" between "an Iranian bomb or the bombardment of Iran".
So what is going on?
In the US, the Bush administration certainly has established war plans for a conflict with Iran, as it has for so many other contingencies.
There are still hawkish voices within the administration who, despite all of the chaos in Iraq, still believe that Iran should be the next target in the Pentagon's sights.
Nonetheless, there still remains considerable leeway for diplomatic action. Much attention is focused on Moscow, the government with the strongest potential "sanction" against Tehran - namely its refusal to supply nuclear fuel for Iran's first power-generating reactor.
In recent weeks though there have been signs that the diplomatic pressure on Tehran has been weakening, just as the Americans in particular are pushing for additional UN Security Council sanctions.
Moscow's position seems less certain, and an agreement in August brokered with the Iranians by the head of the International Atomic Energy Agency, Mohamed ElBaradei , has angered not just the Americans but the three European governments - the UK, France and Germany - who have taken the lead in negotiations with Tehran.
[This] is part of a broader change of diplomatic gear under a young and dynamic president who carries little of the anti-American baggage of his predecessor
Mr ElBaradei's intervention, which has led Iran to accept a plan of action to gradually shed light on its past nuclear activities, is seen by these governments as too lenient.
They say it gives the Iranians yet more time to make a full disclosure of their nuclear programme while failing to insist that they halt uranium enrichment as the UN Security Council has demanded.
The French want to see stronger European Union sanctions whatever the UN might do.
And Mr Kouchner is signalling that France is willing to pay a price by encouraging French firms to limit their dealings with Tehran.
US financial sanctions, both formal and informal, are seen as beginning to have an impact on the Iranian economy. However, critics of such moves argue that this simply panders to the siege mentality of Iranian hard-liners, and rallies popular support around the government in Tehran.
The shift in Paris, though, is significant.
It is part of a broader change of diplomatic gear under a young and dynamic president who carries little of the anti-American baggage of his predecessors.
Since he took office France has announced that combat aircraft supporting Nato operations in Afghanistan will now be based in Kandahar.
IRAN'S NUCLEAR SITES
And there has even been speculation that France might rejoin the alliance's integrated military command, which it walked out of in 1966.
But it is the tougher rhetoric aimed at Tehran which will please Washington the most.
It is bound to cause divisions within the European Union and complicate discussions on Iran within the governing coalition in Germany.
Until now there has been a good deal of talk about Iran's nuclear programme - and some modest sanctions. But the Iranians have largely stayed ahead of the game, pursuing their research activities whatever the wider international community might say.
The French government, for one, is now saying that this situation cannot continue.
The overall message is still diplomatic: the UN and others need to get much tougher towards Tehran.
If they do not then the subtext is clear: the thinly-veiled military threat could become the only alternative.