Romney: I will not let Iran get nuclear weapons

WASHINGTON (Reuters) - Republican presidential candidate Mitt Romney laid down a foreign policy marker on Wednesday, saying that if elected he would not allow Iran to develop nuclear weapons.

An International Atomic Energy Agency report on Tuesday indicated Iran had worked to design nuclear bombs, testing Western powers anew in their standoff with Tehran, which insists it is developing a civilian nuclear program.

Romney, leading some polls of Republican voters in the race to be the party's 2012 presidential nominee, said he would be prepared to work with U.S. allies on a diplomatic solution but would be prepared to act unilaterally if necessary to stop Iran.

"Si vis pacem, para bellum. That is a Latin phrase, but the ayatollahs will have no trouble understanding its meaning from a Romney administration: If you want peace, prepare for war," he wrote in an opinion article for The Wall Street Journal.

He said he would start his presidency by imposing a new round of "far tougher" economic sanctions on Iran "together with the world if we can, unilaterally if we must."

"I will back up American diplomacy with a very real and very credible military option," he said, by maintaining a regular naval presence in the Mediterranean and Gulf region and by increasing U.S. military assistance to Israel.

"These actions will send an unequivocal signal to Iran that the United States, acting in concert with allies, will never permit Iran to obtain nuclear weapons," Romney said.

Successive presidents have attempted to stop or slow Iran's alleged march to a nuclear weapon, but Tehran's leadership has ignored the pressure.

Romney accused President Barack Obama of relying too heavily on international sanctions that had produced little progress.

"Sanctions clearly failed in their purpose. Iran is on the threshold of becoming a nuclear power," Romney wrote.

Obama has had a string of national security achievements, such as the killing of al Qaeda leader Osama bin Laden, which may make it difficult for his 2012 opponent to attack him in that area.

Romney said the Obama administration had done little in response to an alleged Iranian plot to kill Saudi Arabia's ambassador to the United States.

"Only when the ayatollahs no longer have doubts about America's resolve will they abandon their nuclear ambitions," he wrote. (Reporting by Steve Holland; Editing by Peter Cooney)