Mitt Romney pledged to Israel today that he would help protect the country from an Iran armed with nuclear weapons, as he sought to show an aggressive stance in support of a top U.S. ally.

"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 Jerusalem.

"No option should be excluded," the presumptive GOP presidential nominee said. "We recognize Israel's right to defend itself, and that it is right for America to stand with you."

Romney's overseas trip is aimed at showing a contrast with President Obama when it comes to foreign policy. The former Massachusetts governor has been highly critical of Obama's handling of the relationship with Israel and for not doing enough to push back on Iran's efforts to develop a nuclear weapon.

Former White House spokesman Robert Gibbs, an adviser to the Obama campaign, said earlier today on ABC's This Week that the Democratic administration has made "progress" in delaying Iran's nuclear program.

Before Romney's speech, adviser Dan Senor explained to reporters in Israel that the GOP candidate would assert that he would "respect" Israel's right to respond to Iran with military force. Senor issued a statement later appearing to soften that stance, according to the Associated Press, saying that Romney hoped economic and diplomatic sanctions against Iran would work its course.

Arguing that the situation in Iran has gotten worse over the last five years, Romney vowed that blocking the country's nuclear capability would be "our highest national security priority" if he wins the White House.

"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 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."

Romney also drew applause from his audience for proclaiming Jerusalem to be the capital of the Jewish state.

In his remarks to the American Israel Public Affairs Committee in March, Obama warned of rushing to a military option against Iran. "Now is the time to let our increased pressure sink in and to sustain the broad coalition that we have built," Obama told AIPAC.

Obama and his campaign have criticized Romney for seeming quick to want to go to war. Obama has pushed back on Romney's criticisms of his foreign policy, by saying his GOP rival owes Americans a detailed plan on what he would do to address Iran and other crises abroad.

"This is not a game. There's nothing casual about it," Obama told reporters in May. "When I see some of these folks who have a lot of bluster and a lot of big talk ... but when you ask them what they would specifically do, it turns out they repeat some of the things we've been doing over the last three years."

Earlier today, Romney met Israeli Prime Minister Benjamin Netanyahu and Israeli President Shimon Peres. He and his wife, Ann, also visited the Western Wall.

Romney appears to face an uphill challenge in trying to sway Jewish voters. Obama leads Romney, 68% to 25%, among registered Jewish voters, according to the Gallup Poll.

Romney tomorrow will hold a fundraiser in Jerusalem before heading to Poland for another policy speech.