Rarely has his message been as blunt. Denouncing support for terrorism, arming of Iraqi militias and attempts to place the Middle East “under the shadow of a nuclear holocaust”, President Bush accused Iran of threatening the security of nations everywhere. America, he insisted, would “confront this danger before it is too late”. Within hours of his tough message, US forces in Iraq had arrested eight Iranians, searched their luggage and confiscated their Iraqi escort’s weapons before releasing them. American commanders are taking no chances. They know that Iran is smuggling men and weapons into Iraq in huge quantities, arming not only Shia militias but also rival Sunni groups with the express aim of harassing and killing coalition troops.

Iran has made no secret of its malevolent intention to destabilise Iraq and fill the resulting vacuum. President Ahmadinejad boasted earlier this week that the Americans were on the run, and said that when they pulled out they would leave an opening for his forces. “Today you are prisoners in your own quagmire,” he said, demonstrating the hubris that, since the fall of Saddam Hussein, has increasingly marked Iranian behaviour. Some of his top advisers use language even more menacing: the US forces were now “hostages” in Iraq, and would be attacked if the US ordered any military action against Iran, one senior official recently told Western analysts.

Clearly, Iran now believes it can profit from confrontation, which hardliners around President Ahmadinejad appear to be actively seeking. For the past six months, Washington has warned Iran to stop supplying weapons to the insurgents in Iraq. The response has been not only a contemptuous denial but also the dispatch of Iranian Revolutionary Guards to other areas of confrontation. Iranian officials have also admitted that they are supplying weapons to the Taleban in Afghanistan – not because they support these Sunni extremists who were their deadly enemies when in power, but in order to prevent a US and Nato victory that would increase Western influence.

Iran would do well to listen not only to the words but also the tone of Mr Bush’s latest warning. Anger, exasperation and frustration at Iran’s failure to rein in its export of terrorism or to curb its push for a nuclear capability are changing the balance of the debate in Washington. Those who urge further United Nations sanctions, a search for a diplomatic solution and the isolation of Tehran’s hardliners can point to little success. Those who argue that Mr Bush must destroy Iran’s nuclear programme before he leaves office are being balanced by the intense concern in Israel and by Iran’s own arrogant behaviour.

If Iran is deaf to warnings from Washington, it should not ignore the tough new language in Europe. With unambiguous clarity, President Sarkozy said on Monday that a nuclear-armed Iran was unacceptable; unless the world reined in its programme, the only alternative was “an Iranian bomb or the bombing of Iran”. His language was aimed as much at Russia and China as Tehran. Both have posed as Iran’s friends and protectors to shield it from UN sanctions. Both should be realistic. Russia does not want another nuclear power on its southern flank. China is deeply worried about chaos in Afghanistan. It is time thatn it, too, confronted Iran.