US presidential candidate Mitt Romney on Sunday declared Jerusalem to be the capital of the Jewish state and told an Israeli audience that the United States has "a solemn duty and a moral imperative" to block Iran from achieving nuclear weapons capability. Related articles: Romney: Obama undermines Israeli leaders Aide: Romney would back Israel if it strikes Iran US defense law to equip Israel with refueling jets "Make no mistake, the ayatollahs in Iran are testing our moral defenses. They want to know who will object and who will look the other way," Romney said during a speech in Jerusalem's Mishkenot Sha'ananim neighborhood. "We will not look away nor will our country ever look away from our passion and commitment to Israel." Romney meets Peres (Video: Eli Mandelbaum, Avi Peretz) The presidential election hovered over the speech, with the Old City forming a made-for-television backdrop behind Romney, while some of his campaign donors listened in the audience. In a thinly veiled jab at President Barack Obama's administration, Romney said any public differences between the United States and Israel only embolden adversaries. Romney-Fayyad meeting (Video: Reuters) The US presidential candidate said it is a "basic truth" that the United States and Israel will always stand together. Without mentioning the tensions between Obama and Israel's leaders, Romney suggested that the diplomatic differences only encourage Israel's enemies. Obama has, at times, broken with Israel's leaders and called on Israel to follow through on its commitments, such as to halt building of housing settlements in the West Bank. Romney stressed that he would never criticize Israel and would be a steadfast ally to the Jewish state. Jerusalem Mayor Nir Barkat wished the Republican candidate a successful visit to Jerusalem, which he also called Israel's undivided capital. Romney, who earlier in the day with Prime Minister Benjamin Netanyahu and President Shimon Peres, said he felt honored to visit a nation that suffered the most heinous crime (Holocaust) and became a developed democratic country. He called Iran a leader in exporting terror and instability. Prior to delivering his speech in Jerusalem, Romney met with Palestinian Prime Minister Salam Fayyad. The presidential hopeful did not meet with Palestinian President Mahmoud Abbas. Omri Efraim and Elior Levy contributed to the report Follow Ynetnews on Facebook and Twitter Receive Ynetnews updates directly to your desktop