US Secretary of State Hillary Clinton said on Sunday that Iran would not be allowed to have a nuclear weapon and reiterated Washington's commitment to protect close ally Israel from any threat posed by Tehran.
"Your (Iran's) pursuit is futile," she told NBC's "Meet the Press" program, adding that Iran did not have the right to develop a nuclear weapon.
"It is unacceptable for Iran to have nuclear weapons," she added.
Clinton annoyed ally Israel last week by saying the United States would cope with a nuclear Iran by arming its allies in the Gulf and extending a "defense umbrella" over the region.
She implicitly urged Israel to give US policy on Iran's nuclear ambitions a chance to work, saying that Washington remained ready for dialogue with Tehran on its nuclear program.
Clinton added that her country hoped the Jewish state understands American attempts to talk to Iran is a better approach than a military strike.
No interest in White House
During Sunday's interview, it appeared that there was no such thing as a simple yes or no when it comes to Clinton and questions about another run for the White House.
Clinton, 61, seemed to go further than she had previously in shutting the door to another presidential campaign, following her defeat for the Democratic nomination last year by Barack Obama.
"Well, you know, I say no, never, you know, not at all. I don't know what, what else to say," Clinton said after host David Gregory noted that she left some wiggle room in an interview last week in Thailand.
But then Gregory followed up by asking, "Are you saying you wouldn't entertain another run?"
Clinton's response was less clear: "I have absolutely no belief in my mind that that is going to happen, that I have any interest in it happening. You know, as I said, I, I am so focused on what I'm doing."
In the interview on Thai television, Clinton said, "I don't know, but I doubt very much that anything like that will ever be part of my life."
Asked for her views on a preemptive Israeli strike against Iran, Clinton reiterated Israel's right to defend itself and said it would not listen to other nations if it believed its survival were threatened.
But she stressed that pursuing intensive diplomacy with Iran was the best approach, a shift from the Bush administration which avoided engagement with Tehran and insisted that Tehran give up sensitive nuclear work first.
"We will continue to work with all of our allies, and most particularly Israel, to determine the best way forward to prevent Iran from becoming a nuclear state," she said.
A senior Israeli official said the United States should focus on preventing Iran from getting a nuclear weapon rather than talking as if this may be a fait accompli.
"We are not talking in specifics, because that would come later if at all. My view is you hope for the best, plan for the worst," said Clinton on Sunday, defending the comments she made while in Thailand last week.
Several senior US officials, including Defense Secretary Robert Gates and national security advisor James Jones, will be in Israel this week, seeking to reassure the Jewish state.
"We have a long, durable relationship with Israel. We believe strongly that Israel's security must be protected," said Clinton when asked about her comments on the nuclear umbrella concept.
But she also stressed that Washington was committed to a "diplomatic path" with Iran, a shift from the Bush administration which avoided engagement with Tehran until it had given up sensitive nuclear work.
Major powers suspect that Iran is seeking to build a nuclear bomb. Iran says its nuclear work is to generate much-needed power and strongly rejects that it wants to build a weapon.
The Associated Press and Reuters contributed to this report