Romney said in a highly anticipated speech in Jerusalem that the combination of vehement hatred of Israel and the development of nuclear weapons made Iran a major threat that both nations would stand up to.
It would be foolish not to take Iran's leaders at their word," Romney said. "They are, after all, the product of a radical theocracy.
"The regime in Iran is five years closer to developing nuclear weapons capability," Romney said. "Preventing that outcome must be our highest national security priority."
Romney said the United States would stand firmly behind Israel amid the overall turmoil in the Middle East and predicted a more hands-off stance by Washington would only lead to tragedy.
"We have seen the horrors of history. We will not stand by. We will not watch them play out again," Romney said.
Romney called preventing the development of nuclear weapons by Iran "our highest national security priority." But he did not raise the prospect of joint military action against the Iranian regime.
Earlier, however, Prime Minister Benjamin Netanyahu told reporters Romney had assured him in a private meeting that his administration would consider Iran's nuclear program "the greatest danger facing the world."
Romney's senior security adviser, Dan Senor, told reporters that while the campaign did not have access to all U.S. intelligence on Iran, a preliminary policy was based on a not-so-veiled warning to Tehran, the Los Angeles Times said. "[Romney] believes that at this point the only thing that could focus and force the minds of the Iranian leadership on ending their nuclear weapons, their path to a nuclear weapons capability, is the belief that the alternative is far worse," Senor said.