According to the Press Association, the chief UN nuclear inspector criticised talk of attacking Iran as "hype", saying the use of force should only be considered as a last resort and only if authorised by the UN Security Council.
"I would not talk about any use of force," said Mohamed El-Baradei, the head of the International Atomic Energy Agency, in an indirect response to French warnings that the world had to be prepared for the possibility of war in the event that Iran obtains atomic weapons.
Saying only the UN Security Council could authorise the use of force, El-Baradei urged the world to remember Iraq before considering any similar action against Iran.
"There are rules on how to use force, and I would hope that everybody would have gotten the lesson after the Iraq situation, where 70,000 innocent civilians have lost their lives on the suspicion that a country has nuclear weapons," he told reporters.
He was alluding to a key US argument for invading Iraq in 2003 without Security Council approval - that Saddam Hussein had weapons of mass destruction, including nuclear arms.
Four years later, no such arsenals have been found.
El-Baradei, speaking outside a 144-nation meeting of his agency, urged both sides to back away from confrontation, in comments addressed both to Iran and the US-led group of nations pressing for new UN sanctions for Iran's refusal to end uranium enrichment.
"We need to be cool," he said, adding: "We need not to hype the issue."
Later, US Republican presidential contender Mitt Romney said Iran's president Mahmoud Ahmadinejad should not be allowed to address the UN General Assembly next week, but instead should be greeted "with an indictment under the Genocide Convention".
Romney routinely talks about the threat the US faced from "radical jihadists," and he has staked out a hardline position against Iran in particular.