By Jonathan Marcus
BBC diplomatic correspondent
There is no doubting the frustration and dismay of the Europeans who since late 2004 have sought to broker a deal under which Iran would give up its plans to manufacture nuclear fuel.
Iran's confidence today may reflect a changed diplomatic situation
And there's no doubting the anger and alarm in Washington where there is a strong belief - shared by at least some European governments - that Iran will ultimately use its enrichment capability to process material for a nuclear bomb.
But diplomacy is not a zero sum game.
It's more a war of position. And this explains why Iran's action and the responses to it have, so far, been carefully calibrated.
Tehran's new confidence
The EU-Iranian negotiations have served both sides' interests. The Europeans clearly obtained a delay in Iran's uranium enrichment programme.
But paradoxically Iran may have gained more.
Iran's nuclear activities were always going to provoke tensions. But - seen from Tehran - the timing of any crisis was important.
In the Autumn of 2003 Iran was under huge pressure. The UN's nuclear watchdog - the IAEA - was harshly critical of its lack of transparency.
The United States' rapid victory over Saddam Hussein's armed forces had bolstered US confidence and some in Washington wondered if Iran would be the next target for regime change.
Today things are very different.
While some outstanding questions remain, Iran may have explained sufficiently to encourage some IAEA Board members to give it more time.
The United States has huge problems in Iraq and is well aware that Iran could significantly inflame tensions there.
So if there is to be a crisis, then the Iranians may well believe that the context today gives them a significantly stronger hand.