JERUSALEM—Speaking against the backdrop of the historic Old City, Mitt Romney signaled he supports Israel's right to "defend itself" against its enemies and said "any and all measures" should be considered in the world's efforts to stop Iran from developing a nuclear weapon.

The Republican candidate said preventing a nuclear Iran should be America's "highest national security priority." And while he argued that diplomatic efforts should continue, Romney insisted that all options should be on the table in dealing with Iran, including a military strike.

"We should employ any and all measures to dissuade the Iranian regime from its nuclear course, and it is our fervent hope that diplomatic and economic measures will do so," Romney said in an outdoor speech at Mishkenot Sha'anamim, a cultural center in Jerusalem. "In the final analysis, of course, no option should be excluded. We recognize Israel's right to defend itself, and that it is right for America to stand with you. "

Romney pushed back against criticism that those arguing in favor of leaving the military option open are "reckless and provocative and inviting war." "The opposite is true. We are the true peacemakers," Romney said.

He argued that the threat of military action would put more pressure on the ayatollahs in Iran, whom he accused of "testing our moral defenses."

"They want to know who will object and who will look the other way," Romney said. "My message to the people of Israel and the leaders of Iran is one and the same: I will not look away, and neither will my country."

In a message sure to appeal to Jewish voters, with whom Republicans are aiming to make inroads ahead of November's election, Romney repeatedly emphasized the "shared values" and "shared interests" between the United States and Israel.

Romney avoided directly criticizing President Barack Obama but slipped in a dig at his Democratic rival, arguing that public differences between the U.S. and Israel only embolden Israel's enemies.

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"We cannot stand silent as those who seek to undermine Israel, voice their criticisms. And we certainly should not join in that criticism," Romney said. "Diplomatic distance in public between our nations emboldens Israel's adversaries.

By history and by conviction, our two countries are bound together. No individual, no nation, no world organization, will pry us apart. And as long as we stay together and stand together, there is no threat we cannot overcome and very little that we cannot achieve."

Romney is dining with Israeli Prime Minister Benjamin Netanyahu on Sunday night. On Monday, he'll headline a major fundraiser for his campaign among top Jewish supporters, many of whom were in the audience for Sunday's speech. Among those in attendance: Las Vegas casino magnate Sheldon Adelson, who has contributed millions of dollars to a pro-Romney super PAC.

On Monday afternoon, Romney heads to Poland, the final stop on his weeklong overseas tour.