US Republican presidential candidate Mitt Romney would back Israel if it were to decide it had to use military force to stop Iran from developing a nuclear weapon, a senior aide said on Sunday.

"If Israel has to take action on its own, in order to stop Iran from developing that capability, the governor would respect that decision," Romney's senior national security aide Dan Senor told reporters traveling with the candidate.

The comment made ahead of Romney's planned meetings in Jerusalem with Israeli leaders seemed to differ with US President Barack Obama's attempts to convince Israel to avoid any preemptive attack.

Senor told reporters that Romney believed the threat from Iran was approaching on a path involving two timelines.

The first was Iran's drive - denied by Tehran - to develop a nuclear weapons capability, and the second was having the ability to penetrate Iran's defenses before they were hardened in such a way to protect against a strike, Senor said.

In excepts of a speech Romney was to deliver on Monday evening, the former Massachusetts governor planned to say that an aggressive approach to Tehran was needed to protect against a threat to the very existence of Israel, the closest US ally in the turbulent Middle East.

"When Iran's leaders deny the Holocaust or speak of wiping this nation off the map, only the naïve - or worse - will dismiss it as an excess of rhetoric," he would say.

"Make no mistake: The ayatollahs in Tehran are testing our moral defenses. They want to know who will object, and who will look the other way."

Romney was set to kick off the official portion of his visit to Israel Sunday morning in a 10:40 a.m. meeting with Prime Minister Binyamin Netanyahu, followed by additional meetings with President Shimon Peres, Labor leader Shelly Yechimovich, Kadima leader Shaul Mofaz and Palestinian Authority Prime Minister Salam Fayyad.

Romney and Netanyahu will meet again later in the day after the Tisha Be’av fast when he and his wife, Ann, will dine at the Prime Minister’s Residence with Netanyahu and his wife, Sara.

Netanyahu and Romney are not scheduled to hold any significant joint public appearances, with the prime minister very keen on not being perceived in any way as intervening in the US elections.

Romney’s visit to Israel – his fourth – is widely considered an effort to woo pro-Israel voters in the US, both Jews and Evangelical Christians, many of whom are discontent with the Middle East policies of President Barack Obama.

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Romney arrived in Israel on Saturday night on the second leg of a three-country tour that began in London, where he badly annoyed his hosts by questioning whether the city was ready for the Olympics.

Romney is slated to leave for Poland at about noon on Monday.

Before taking off, he is scheduled to host a fund-raiser at the King David Hotel in Jerusalem Monday morning. The event was moved from Sunday evening to Monday morning so as not to conflict with Tisha Be’av. The cost to attend the event, where Romney is expected to appear for 45 minutes, is $50,000 a couple.

Herb Keinon contributed to this report.

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