Leading article: This is no time for sabre-rattling

Rhetorical subtlety has never been George Bush's forte, and a hall-full of reliably patriotic veterans has long been his audience of choice. But the verbal onslaught he launched on Iran before the American Legion in Nevada this week took his post-Iraq sabre-rattling to a new, more dangerous, level.

It is true that Mr Bush regularly blames Iran when US efforts in Iraq are stalling, and the degree of Iran's villainy tends to be magnified in proportion to US setbacks. Yet the terms in which Mr Bush couched his speech to veterans in Reno were especially inflammatory.

Taking Iran to task for attacks on US troops and Iraqi civilians, Mr Bush appeared to threaten direct reprisals. "I have authorised our military commanders in Iraq," he said, "to confront Tehran's murderous activities."

He also broached Iran's nuclear ambitions, claiming that its "active pursuit of technology that could lead to nuclear weapons" could cast "the shadow of a nuclear holocaust" over the whole region. Iran's actions, he said, threatened the security of nations everywhere. "We will confront this danger before it is too late."

Mr Bush's speech came less than two weeks after reports that the White House was planning to designate Iran's Revolutionary Guards a terrorist organisation. If this happens, anything untoward that Iran does can be defined as "state-sponsored terrorism" by the US – so precipitating perhaps a military response.

Given the long absence of conventional diplomacy between two countries that now have so much to talk about, it is perhaps not surprising that the megaphone variety is currently the order of the day. It is even possible, though he did not admit as much, that Mr Bush was responding to a speech by President Mahmoud Ahmadinejad, who claimed that the US was on the verge of collapse in Iraq and that Iran was standing ready to help fill the vacuum.

We would like to be able to dismiss all this as good knockabout stuff that allows both sides to let off some steam. But the lesson from Iraq is that where two headstrong and ideologically-driven leaders shout accusations past each other, words graduate all too rapidly into deeds. Nor can it be denied that Iran has a legitimate interest in the future of Iraq, whereas the justification for the US invasion remains contestable at very least.

The MPs who are lobbying for Britain to keep out of this dispute are right. If Britain has a role, it should be to spearhead a return to constructive engagement. Not so long ago US envoys met Iranian officials to discuss regional co-operation on Iraq. It is on such practicalities that energies should be concentrated. Sabre-rattling holds too many risks.