UK Foreign Secretary Jack Straw has said it is "inconceivable" that America would try to bomb Iran.
Mohammad Khatami has offered a compromise in nuclear talks
There has been speculation about whether the newly re-elected George Bush will be more hawkish over Iran.
Pointing to talks with Tehran, Mr Straw said: "I don't see any circumstances in which military action would be justified against Iran, full stop."
Mr Straw said President Bush's re-election gave the world the chance to make new progress on Middle East peace.
No more war?
After months of talks, Iranian president Mohammad Khatami this week said Iran was ready to pledge not to pursue nuclear weapons.
But he wants recognition of Iran's right to peaceful nuclear technology.
Asked if it was inconceivable that the world would support US military action against Iran, presumably bombings or using Israel as a "proxy", Mr Straw replied: "Not only is that inconceivable but I think the prospect of it happening is inconceivable."
He told BBC Radio 4's Today programme the US had been part of the consensus on pursuing the negotiations with Tehran and there was no reason to think that would change.
The chances of another conflict in the wake of the Iraq war "pretty remote", he said.
"I don't think, please God, that we are going to see in the next four years the most cataclysmic event for international relations that we have seen in 60
years which occurred on 11 September 2001," he said.
He believed the international divisions which had followed the terror attacks could be healed.
'Chance for progress'
Mr Straw said everybody should recognise that America had come to a "very clear democratic result" in re-electing President Bush, and try to work with the US.
"It is actually a moment of opportunity for the democratic world
to come together and to work on items and issues, particularly the Middle East,
on which we have seen frustratingly small progress in recent years," he argued.
Mr Straw said Foreign Office officials were continuing to examine the accuracy of The Lancet medical journal's estimates that the Iraq war has led to 100,000 extra deaths.
Tony Blair has spoken to both President Bush and Senator Kerry
Estimates of casualties varied greatly, he said, with groups such as Iraq Body Count suggesting about 15,000 civilians had been killed by military intervention in Iraq.
Critics of the war are particularly concerned about the prospect of a major assault on Falluja by the US-led force in Iraq.
Mr Straw said the Iraqi interim government was seeking a political solution to the problems in the insurgent-held city.
But it was necessary to tackle the "nest of terrorists" in the area, just as had happened in Afghanistan to pave the way for democratic elections, he added.
In the US polls, Democratic challenger John Kerry conceded defeat on Wednesday evening and in his victory speech President Bush said he wanted to reach out to all Americans.
Tony Blair has spoken to both President Bush and Senator Kerry.
The prime minister said he looked forward to continuing his strong relationship with the president during his second term in the White House.
The international community had to be brought together, said Mr Blair, stressing the need for action on poverty, the Middle East and the conditions exploited by terrorists.
It was a message he repeated at Thursday's Cabinet meeting and he will discuss the election result with European leaders when he flies to a summit in Brussels later in the day.
His spokesman said: "The prime minister does believe we need to use this as
an opportunity to rebuild the relationship across the Atlantic."