Secretary of State Hillary Clinton today outlined how the United States might cope with a nuclear Iran - by arming its allies in the Gulf and extending a "defence umbrella" over the region.
She later said she was not suggesting a new policy and reiterated that Iran possessing nuclear weapons would be unacceptable.
Speaking first in Bangkok, Mrs Clinton said crossing the nuclear threshold would not make Iran, which Washington believes is pursuing nuclear weapons, safer. Iran says its nuclear programme is to generate electricity so it can export more oil and gas.
"We will still hold the door open (for talks with Iran) but we also have made it clear that we'll take actions, as I've said time and time again, crippling action, working to upgrade the defence of our partners in the region," she said in a programme taped for Thai television ahead of Asia's biggest annual security meeting, being held in the resort of Phuket.
“We want Iran to calculate what I think is a fair assessment ... that if the US extends a defence umbrella over the region, if we do even more to support the military capacity of those in the Gulf, it's unlikely that Iran will be any stronger or safer because they won't be able to intimidate and dominate as they apparently believe they can once they have a nuclear weapon."
A senior US official said Mrs Clinton's comments should be seen as public arguments that the United States is making to dissuade Iran from pursuing nuclear arms rather than a sign that the United States is becoming resigned to the prospect.
Asked later at a news conference in Phuket to flesh out what she meant by a defence umbrella, Ms Clinton said: "I was simply pointing out that Iran needs to understand that its pursuit of nuclear weapons will not advance its security or achieve its goals of enhancing its power both regionally and globally.
"The focus that Iran must have is that it faces the prospect if it pursues nuclear weapons of sparking an arms race in the region. That should affect the calculation of what Iran intends to do and what it believes is in its national security interest because it may render Iran less secure, not more secure."
Israeli deputy prime minister Dan Meridor, reacting to Clinton's earlier comments, said it would be far better to prevent Iran from crossing the nuclear threshold than to try to counter it with a defence umbrella.
"I was not thrilled to hear the American statement ... that they will protect their allies with a nuclear umbrella, as if they have already come to terms with a nuclear Iran. I think that's a mistake. I think it would be more appropriate not to accept the premise that Iran has turned nuclear but to try to prevent this," Mr Meridor told Israel's Army Radio.
Last week Mrs Clinton said Iran's intentions were unclear following June's election there and that President Barack Obama's offer of talks with Tehran over its nuclear programme was not open-ended.
Despite the US policy shift, Iran has not responded to Mr Obama's overtures and those from other countries seeking to persuade Tehran to give up sensitive nuclear work the West believes is aimed at building a bomb and Iran says is to generate power. Diplomats suspect Iran is buying time by stalling over getting into any substantive talks.