Iran is presenting a fundamental challenge to the Bush administration's diplomacy.
By Jonathan Marcus
BBC Defence correspondent
Under scrutiny: Reporters look at a model of Iran's nuclear plant
Its foreign minister has said that once relations with the UN nuclear watchdog, the IAEA, are "normalised", Iran will resume its uranium enrichment activities.
The United States firmly believes that Iran has no real need for a nuclear power programme and is intent on gathering the building-blocks for a nuclear weapon.
America's European allies share many of its concerns, but not Washington's certainty.
They have encouraged the Bush administration to pursue a multilateral approach to dealing with Iran, by offering more carrot than stick as it cajoles and encourages Tehran to open up all of its nuclear activities to international inspection.
So far, all the signs coming from the IAEA meeting in Vienna suggest the US is willing to go along with this approach.
But the threats from the Iranian Foreign Minister to resume uranium enrichment activities will not be viewed as helpful.
Such a capability is seen as an essential element in a free-standing weapons programme, though Iran insists that its enrichment programme is for peaceful purposes.
Foreign minister Karrazi says Iran is entitled to a nuclear programme
That will not cut much ice in Washington, but nor will Mr Bush relish a showdown with Iran in an election year.
Some argue that, in the wake of the invasion of Iraq and the continuing strain on US resources, a new more conciliatory foreign policy is emerging in Washington.
This - a kind of Bush Mark II - is more explicitly multilateral.
And the administration's approach to Iran is perhaps a good example of this eagerness to act with allies.
But there are limits. Critics say the Bush administration has lost none of its ideological edge.
Going along with the Europeans on Iran may be convenient for now.
But Iran's own actions could profoundly test this new Bush approach, leading to a much more confrontational position.