US President George W Bush has vowed to respond firmly if Iran foments violence inside Iraq.
Washington has accused Tehran of undermining efforts to stabilise Iraq and of pursuing nuclear weapons.
Two US aircraft carriers have been stationed in the Gulf as a warning to the Islamic republic.
Some war critics say the Bush administration's language on Iran echoes comments made leading up to the 2003 invasion of Iraq.
But Mr Bush said his intention is to protect US troops, and not to invade Iran.
