UK Prime Minister Tony Blair has said that diplomacy, not military action, is the best way to resolve the stand-off over Iran's nuclear programme.
He told the BBC he was not aware of any plans to attack Iran and said the only viable solution was a political one.
But he said he could not "absolutely predict every set of circumstances".
There has been tension with Tehran over its nuclear programme - which it claims is for fuel, not weapons - and its alleged role in Iraq's violence.
US officials recently displayed what they say is proof Iran is giving weapons to Shia militias in Iraq.
Democrats say they see parallels with the run-up to the Iraq war, when the US made a case for action on the basis of weapons which were never found.
But Mr Bush has dismissed such speculation of an attack as "noise" by his critics.
On Thursday, Mr Blair told BBC Radio 4's Today programme: "Iran is not Iraq.
"There is, as far as I know, no planning going on to make an attack on Iran and people are pursuing a diplomatic and political solution, for a very good reason incidentally, that it's the only solution anyone can think of that is viable and sensible."
Foreign Secretary Margaret Beckett said: "We remain determined to prevent Iran acquiring the means to develop nuclear weapons."
On Wednesday Iranian president Mahmoud Ahmadinejad said Iran would try to achieve nuclear capability as soon as possible, as a UN deadline for Tehran to freeze its uranium enrichment programme expired.
He said those countries calling on Iran to halt its nuclear programme should shut down their own facilities for producing nuclear fuel.
Last year Iran resumed uranium enrichment - a process that can make fuel for power stations or, if greatly enriched, material for a nuclear bomb.
Tehran insists its programme is for civil use only, but Western countries suspect Iran is trying to build nuclear weapons.