Increasingly tough talk on Iran from the Bush administration – with vice-president Dick Cheney warning of the “growing threat” from the Islamic republic – has rattled politicians and diplomats in Washington worried that the war in Iraq is set to widen.

While few lay claim to understanding what George W. Bush has in mind, there is a widespread sense that the likelihood of some kind of military clash or conflict with Iran – directly or through proxies – has risen since the US president accused Tehran last week of “providing material support for attacks on American troops” in Iraq.