JERUSALEM -- Mitt Romney would respect an Israeli decision to make a unilateral military strike against Iran aimed at preventing Tehran from obtaining nuclear capability, a top foreign policy adviser said Sunday as he outlined the aggressive posture the Republican presidential candidate will take toward Iran in a speech in Israel later in the day.
Romney has said he has a "zero tolerance" policy toward Iran obtaining the capability to build a nuclear weapon.
"If Israel has to take action on its own, in order to stop Iran from developing the capability, the governor would respect that decision," foreign policy adviser Dan Senor told reporters ahead of the speech, planned for late Sunday near Jerusalem's Old City.
Senor said Romney is careful to note the governor believes preventing nuclear "capability" -- not just a nuclear weapon -- is critical.
He later clarified his comments in a written statement, saying: "Gov. Romney believes we should employ any and all measures to dissuade the Iranian regime from its nuclear course, and it is his fervent hope that diplomatic and economic measures will do so. In the final analysis, of course, no option should be excluded."
Democratic U.S. President Barack Obama has also affirmed the right of Israel to defend itself, but in contrast to Romney, Obama has warned of the consequences of an Israeli strike on Iran.
"Already, there is too much loose talk of war," Obama told the American Israel Public Affairs Committee in March. "Now is the time to let our increased pressure sink in and to sustain the broad international coalition we have built."
Pentagon officials have spoken publicly about the difficulty of such a strike and American officials have expressed concern about the destabilizing effect such military action could have in the region, even if carried out successfully.
Romney, like Obama, believes the option of a U.S. attack should also be "on the table." He has said he will do "the opposite" of what Obama would do in his approach to Israel.
"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 plans to say later Sunday in a speech in Jerusalem. "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."
The Obama administration hasn't ruled out the military option, but Obama has so far been relying on economic sanctions and diplomatic negotiations to discourage Iran from building a nuclear bomb.
For its part, Iran says it is not interested in nuclear weapons and its nuclear program is for peaceful, civilian purposes.
The Israelis are considering a strike because they fear Iran could be moving its nuclear enrichment sites further underground, out of reach of the weapons Israel has available.
Israeli Prime Minister Benjamin Netanyahu on Sunday welcomed Romney as "a representative of the United States" and told the Republican presidential candidate he agrees with his approach to the threat of a nuclear Iran.
Netanyahu said he listened to Romney's speech in Reno, Nev., where the likely GOP nominee said that Iran possessing nuclear capability is the greatest danger facing the world.
"Mitt, I couldn't agree with you more," Netanyahu told Romney.
"We have to be honest and say that all the sanctions and diplomacy so far have not set back the Iranian program by one iota. And that's why I believe that we need a strong and credible military threat coupled with the sanctions to have a chance to change that situation," Netanyahu said.
Romney's verbal support for unilateral Israeli military action represents a break from Obama administration policy.
Iran's nuclear program has become the most pressing problem for the U.S. and Israel and Republicans have consistently criticized Obama for putting too much pressure on Israel in the peace process and being too weak on Iran.
Obama rejects the criticism, and his aides point to what they call unprecedented U.S.-Israeli security cooperation.
Senor was previewing the speech Romney plans in Jerusalem after he spends the day meeting with Israeli officials.
Over the course of the day, Romney will confront some of the world's most difficult peace and security challenges as he looks to demonstrate to Jewish and evangelical voters back home that he's a better friend to Israel than Obama.
Romney faces high stakes as he begins his talks with top Israeli officials and meets with the Palestinian prime minister. Mindful of polls back home that show a tight presidential contest, the former one-term Massachusetts governor is looking to burnish his foreign policy credentials and prove his mettle as a possible commander in chief.
The trip is a chance for Romney to draw implicit contrasts with Obama and demonstrate how he would lead America on the world stage.
But Romney arrived in Jerusalem Saturday night after a difficult few days in Britain, where he made the mistake of criticizing the country's Olympic Games and raised the hackles of his hosts. The gaffe undermined the stated goal of his weeklong journey through Britain, Israel and Poland: emphasizing America's ties with longstanding allies.
Romney has pledged not to criticize Obama while on foreign soil, honoring longstanding American tradition of leaving politics at the water's edge. But his aide's announcement of Romney's willingness to express support for an Israeli strike while in Jerusalem represents an effort to contrast the two presidential opponents.
In addition to Netanyahu, Romney met with other Israeli officials and will also sit down with Palestinian Prime Minister Salam Fayyad.
"Like you we are very concerned about the development of nuclear capabilities on the part of Iran and feel it is unacceptable for Iran to become a nuclear armed nation," Romney said at a meeting with Israeli President Shimon Peres. "The threat it would pose to Israel, the region and the world is incomparable and unacceptable."
Romney planned to spend the evening dining at Netanyahu's home -- the Israeli leader invited Romney and his wife to break the fast for the Jewish holiday Tisha B'Av. The holy day, celebrated Sunday, commemorates the destruction of two temples in Jerusalem.
Romney and Netanyahu have known each other since both were young businessmen at Boston Consulting Group in the 1970s.
While Romney is left to implicit contrasts with his Democratic opponent, Obama has been focusing on Israel, signing legislation on Friday increasing military and civilian ties between the U.S. and Israel. And he authorized the release of an additional $70 million in military aid for Israel, a previously announced move that appeared timed to Romney's trip.