Mitt Romney meets Binyamin Netanyahu to discuss Iran's nuclear programme Reuters

Mitt Romney would back unilateral military action by Israel against Iran's nuclear sites, a senior aide said as the presumptive Republican candidate embarked on a series of high-level meetings in Jerusalem.

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

Romney arrived in Israel on Saturday evening for a brief visit, during which he will meet the Israeli prime minister, Binyamin Netanyahu, and president, Shimon Peres, as well as the Palestinian prime minister, Salam Fayyad. The visit is aimed at reinforcing Romney's support for Israel and his personal friendship with Netanyahu, and appealing to Jewish voters in the US ahead of November's presidential contest.

He will also make a speech on Sunday on foreign policy and US-Israeli relations. It is expected to focus on the Iranian nuclear issue and the common interests of Israel and the US.

In comments echoing Netanyahu's position that a nuclear Iran is the biggest threat to the Jewish people since the Holocaust, Romney will say: "We have seen the horrors of history. We will not stand by. We will not watch them play out again."

Preventing the Iranian regime developing a nuclear weapons capability "must be our highest national security priority," Romney will say according to excerpts of the speech released in advance. "The security of Israel is in the vital national security interests of the United States."

Romney is seeking to sharply differentiate his position from that of President Obama, who has urged caution on Israel's leaders regarding a military strike against Iran. Sanctions and diplomacy must be given time to reap results, Obama has said.

However, a report in the Israeli daily Haaretz said a senior US official briefed Netanyahu on America's contingency plans for possible military action in the event of sanctions and diplomacy failing.

National security adviser Tom Donilon, who visited Israel two weeks ago, shared details of the preparations, including US weaponry and military capability for striking underground facilities, during a three-hour meeting with the Israeli prime minister, according to the report which was sourced to "a senior American official".

The timing of the story suggests a desire by the administration to pre-empt Romney's presentation of himself as a more robust supporter of tough action against Iran.

However, the report was denied by a senior Israeli official. "Nothing in the article is correct. Donilon did not meet the prime minister for dinner, he did not meet him one-on-one, nor did he present operational plans to attack Iran," said the official, speaking anonymously.

Romney's efforts to win over American Jewish voters are having limited success, according to a recent opinion poll, which puts support for Obama at 68% among US Jews compared with 25% for the Republican candidate. Although a drop from the 75% of American Jews who backed Obama in the 2008 election, the latest figures also represent sliding support for Romney compared with a Gallup poll in June, which gave 29% of the Jewish vote to the Republican and 64% to Obama.

Romney has attacked the US president – who has not visited the Jewish state since his election – for publicly criticising Israel. Although custom dictates that presidential candidates refrain from criticising their opponents while abroad, in his speech Romney will reiterate the strong ties between the US and Israel.

"We're part of the great fellowship of democracies. We speak the same language of freedom and justice, and the right of every person to live in peace. We serve the same cause and provoke the same hatreds in the same enemies of civilisation," he will say.

Romney's visit falls on the Jewish religious day of Tisha B'Av, a day of fasting and mourning the destruction of the First and Second Temples. A fundraising event had to be postponed until Monday morning when it was realised it had been scheduled before the end of the fast at sunset.

Romney and his wife, Ann, are scheduled to dine with the Netanyahus at their residence on Sunday evening. Netanyahu and Romney have had a warm personal relationship since working together in the US in the 1970s. Following controversy over the candidate's comments on the preparedness of London to host the Olympic Games, his aides will be anxious to avoid further gaffes. Media access to events during the visit has been tightly restricted, and there are expected to be no opportunities to put questions to Romney.

The media has been barred from access to Monday's fund-raiser at the King David Hotel in Jerusalem, at which the minimum donation from participants is $50,000. Among those expected to attend is Sheldon Adelson, a high-profile billionaire Jewish American casino magnate and major supporter of and donor to the Romney campaign. Adelson also owns Israel Hayom, Israel's biggest circulation newspaper, which is distributed free and takes a strong pro-Netanyahu line.

The Romney entourage is to fly to Poland on Monday.