Ryan Crocker, the US Ambassador to Iraq, is a fluent speaker of both Farsi and Arabic whose diplomatic career has spanned most of the Islamic world’s harshest and turbulent regimes. No more formidable interlocutor could have been selected for yesterday’s meeting in Baghdad yesterday with Iran’s Ambassador to Iraq, in the first substantial official contact between the two countries in 27 years. The task fell to Mr Crocker not, however, because of his credentials, but because of the job he holds now. The agenda was Iraq, and Iranian meddling in Iraq. To read into it the beginnings of a diplomatic thaw would be highly premature; only if Iran mends its ways in Iraq would contacts on the rest of the vexed bilateral agenda serve any purpose.

America’s narrow goal was to exact an official Iranian statement of support for the Iraqi Government and a formal pledge to cooperate in stabilising the country – commitments that, Baghdad and Washington hope, would then put Iran on the spot when confronted by the constantly accumulating evidence that it is actively training, arming and funding the enemies of stability, al-Qaeda cells as well as Shia extremists. Mr Crocker got the statements of intentions he sought, but these were predictably accompanied by assertions that Iraq’s troubles stem from the presence in Iraq of US forces, and a flat denial that Iran is arming the insurgency. Cunningly, Iran’s Ambassador then proposed a “trilateral security mechanism” for Iraq: a poisoned chalice, since the creation of any such body would compound Sunni suspicions that Iran’s strategy is to turn Iraq into a puppet state. Mr Crocker observed drily that since there was agreement on policy, no mechanism was needed for Iran to put its principles into practice.

This is almost certainly the opposite of Iran’s true intention. On May 17 Iran’s Supreme Leader, Ayatollah Ali Khamenei, declared that the only purpose of this meeting was “to give them an ultimatum” to withdraw and that Iran would never negotiate with “the arrogant, bullying, expansionist and colonialist Government of the US”.

The gathering congressional mutiny against a long-term American military commitment has convinced Iran’s hardliners that their strategic goal – a US humiliation in Iraq that would render it impotent throughout the Middle East – is in reach. Iranian intelligence and elements of its Revolutionary Guard, both directly controlled by the supreme leadership, have stepped up arms shipments, particularly of the armour-piercing roadside bombs that have been responsible for the majority of American and British deaths. To send the message to Americans that the “surge” is failing to improve security, Iran’s agents have orchestrated high-profile attacks on the green zone in Baghdad. They are arming and financing not only militias and death squads formed by Shia co-religionists in southern Iraq, but also Syrian-backed Sunni jihadists and al-Qaeda networks farther north, groups with which Iran has nothing in common but hatred of the US.

Iraq wanted the US to talk to Iran and Washington did well to oblige. But everything points, as President Bush noted at the weekend, to a deadly summer in Iraq, with violence likely to peak in August as General David Petraeus prepares to deliver his “progress report” to Congress. The more pressure piles on Mr Bush to scale back US force levels thereafter, the less will be the pressure on Iran to call off its dogs. Iran has bet the bank on failing American resolve.