President Bush is not only rejecting the advice of all those who have urged him to talk to Iran. He is also doing the opposite: accusing it of working against the US in Iraq and threatening it with unspecified consequences if it does not stop.

But the chances that Congress would tolerate a military attack are so slim that Tehran can reasonably brush off US threats as unreal.

So the threats are both incredible and provocative. They may also be made to look irrelevant by shifting allegiances in the region. Iran made overtures, of a kind, to Saudi Arabia this week, while the new influence of moderates may make it easier for it to strengthen those relationships, even if it does nothing to curb the Government’s nuclear ambitions.

This week has brought an explicit triple warning for Iran from members of the Bush Administration: Condoleezza Rice, Secretary of State; Robert Gates, Secretary of Defence; and Zalmay Khalilzad, Ambassador to Iraq. Each accused Tehran of working to destabilise Iraq and frustrate US plans. Each also kept this separate from the international alarm over Iran’s nuclear ambitions.

Gates played down the significance of the recent order by Bush to send reinforcements to the region and to deploy Patriot missile defence systems, seen widely as a warning to Iran and Syria. But in the most aggressive statement, Khalilzad said that the US intended to pursue Iran’s “networks” within Iraq.

For the moment, then, the US is staying clear of threatening action against Iran, for all the speculation to the contrary. But it is threatening to take action against those it deems to be Iranian agents within Iraq for any “unhelpful” contribution there.

The pitfalls of this new approach are already clear. The US recently seized people it labelled Iranian agents in the Kurdish-controlled part of Iraq, after a similar raid three weeks ago. But Iraqi ministers have protested that the men were there at the invitation of the Government.

That confronts the US, yet again, with its central problem in Iraq: the Government’s persistent closeness to Iran, and its lack of desire to do what the US wishes. The immediate obstacle is in Baghdad, not Tehran.

The second problem is that there is no weight behind the threats. Scepticism about Bush’s plans for a “surge” of forces in Iraq is so noisy, from his military and the Democrat majority in Congress, that support for military action against Iran is inconceivable. The US’s best hope is that Iran may be changing (and that a falling oil price will convince it of the need to do so).

True, there is no shift — not a fraction — in its determination to press on with its nuclear programme, as President Mahmoud Ahmadinejad has said again. But this week the President and Supreme Leader Ayatollah Ali Khamenei asked Saudi Arabia to help to ease tension with the US. Ali Larijani, Iran’s chief nuclear negotiator, was pictured prominently in Saudi newspapers delivering the letter to King Abdullah.

This attempt may represent Iran’s attempt to undermine support for military action among its neighbours, but it may also provide the basis for a regional effort to stabilise Iraq. It may also reflect the new influence of Iranian moderates, who did unexpectedly well in December polls, although many false dawns have been recorded before.

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