JERUSALEM -- Preventing a nuclear Iran is the "highest national security priority" for the U.S., Republican presidential candidate Mitt Romney said Sunday, and "no option should be excluded" in that pursuit.

With the backdrop of Jerusalem's Old City behind him, Romney sought to strike an aggressive tone and vowed to "stay together and stand together" with Israel as it faces threats from neighboring countries.

Romney's toughest talk was directed at Iran.

"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 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."

Though his speech did not directly criticize President Obama- Romney refused to do so while on "foreign soil" - it did have a few indirect jabs.

"We cannot stand silent as those who seek to undermine Israel voice their criticisms. And we certainly should not join in that criticism," he said, a veiled reference to the sometimes icy relationship between Obama and Israeli Prime Minister Benjamin Netanyahu. "Diplomatic distance in public between our nations emboldens Israel's adversaries."

In the U.S., the Republican National Committee and Romney's campaign spelled out what Romney did not. The RNC sent out a list of newspaper clips detailing the friction between Obama and Netanyahu, and the Romney campaign sent a late afternoon e-mail titled "President Obama's hypocrisy on protecting our allies."

Beyond the tone of his speech, it was unclear how Romney's Israel policy would differ from Obama's. Romney said he supports a "two state" solution to the decades-old problem between Israel and the Palestinians, just as Obama and his predecessors have.

During an interview with CBS News, Romney declined to answer a question about what he would do differently from Obama.

Earlier Sunday, Romney adviser Dan Senor said Romney "would respect" a decision by Israel to attack Iran to stop that nation's nuclear program. Romney backed away from that assertion during some pre-speech interviews and then did not mention such an attack during his address.

While Romney was in London to watch the opening ceremonies of the Olympics on Friday, Obama signed the United States-Israel Enhanced Security Cooperation Act, which will send $70 million in additional military aid to Israel and pay for its Iron Dome missile-defense system.

"We are standing by our friends in Israel when it comes to these kinds of attacks," Obama said.

Romney pledged to move the U.S. Embassy in Israel from Tel Aviv to Jerusalem, a step the past three U.S. presidents have declined to make.

"My understanding is the policy of our nation has been a desire to move our embassy ultimately to the capital," Romney said in an interview on CNN. "That's something which I would agree with - but I would only want to do so and to select the timing in accordance with the government of Israel."

USA Today