On Monday, US President George W. Bush said he could not rule out using force if Washington was unable to persuade Tehran to abandon a nuclear energy programme it charges is cover for developing atomic weapons, while secretary of state-designate Condoleezza Rice called for world action on the issue.

A report in the New Yorker magazine this week said US commandos had been operating inside Iran since mid-2004 to search out potential targets for attack.

Overall, the Bush administration "recognises that a military attack against Iran's military facilities is not a very attractive option", said Gary Samore, a specialist on Iran at the International Institute of Strategic Studies think tank in London.

"There are many drawbacks, both practical and political," Samore told AFP, while adding that the Pentagon was undoubtedly "examining the options for a pre-emptive military strike" against Iran's nuclear and missile facilities.

A game of diplomatic bluff was underway, with Washington hopeful that the threat of military action might pressure Britain and other European Union nations to negotiate forcefully with a worried Tehran so as to head off war, he explained.

"In a way, the American threat to bomb Iran is also indirect pressure on Europe to do its very best, to achieve a diplomatic solution," he said, while adding that Bush would find it extremely difficult to find backing in Europe for military action.

"Even if British officials recognise that the threat of a military attack may help their diplomatic efforts with Iran, I have not been able to find a British official, much less French or German, who think that a military attack actually makes sense," he said.

"My guess is that the British government would at best be silent, at worst be opposed."

Much would depend "on who the British hold responsible for the failure of diplomacy", he added.

"If the British feel that the US has been unreasonable and unsupportive of British diplomatic efforts, then obviously London will be less inclined to support the US."

British Prime Minister Tony Blair, whose popularity has been badly dented by his decision to back the US-led conflict in Iraq, would be extremely wary of getting his nation involved in another conflict, added Katarina Dalacoura from the International Relations department at the London School of Economics.

It "would not make sense for them (the British government) to do that, especially given all the flak they have received over Iraq," she told AFP.

"The EU does have a policy on Iran, it has taken specific steps to contain the nuclear issue and reach an agreement," she explained.

"I think it would be very damaging to relations between Britain and its European partners if they were to go along with the Americans on this... I think Blair would draw a line on Bush, even though he may of course not do it as openly."

Blair's Foreign Secretary Jack Straw has already expressed Britain's wariness at the possibility of war with Iran, saying in November that it was "inconceivable".

"I don't see any circumstances in which military action would be justified against Iran full stop," he told BBC radio.

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