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Marking the 60th anniversary of Israel's founding, President Bush on Thursday said that allowing Iran to possess nuclear weapons is a "betrayal of generations" and pledged that the United States will continue to help protect Israel's sovereignty in the face of any and all threats.

As the U.S. fights two fronts in the War on Terror, Israel faces down threats to its existence from Hamas, Hezbollah, other terror groups as well as nearby terror-supporting states such as Iran, whose leader claims the Jewish state should be blown off the map.

In a speech to the Knesset, or parliament, Bush took special aim at Iran, saying the United States stands with Israel in opposing moves by Tehran to obtain nuclear weapons.

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"Permitting the world's leading sponsor of terror to possess the world's deadliest weapons would be an unforgivable betrayal for future generations," the president said. "For the sake of peace, the world must not allow Iran to have a nuclear weapon."

The president, without naming names but possibly referring to Democratic presidential candidate Barack Obama or former President Jimmy Carter, said anyone who claims that talking with terrorists will result in peace is experiencing a "foolish delusion"

"Some seem to believe we should negotiate with terrorists and radicals, as if some ingenious argument will persuade them they have been wrong all along. We have heard this foolish delusion before.

"As Nazi tanks crossed into Poland in 1939, an American senator declared: 'Lord, if only I could have talked to Hitler, all of this might have been avoided.' We have an obligation to call this what it is — the false comfort of appeasement, which has been repeatedly discredited by history," he said, referring to Idaho Republican Sen. William Borah.

Responding to the criticism, Obama immediately responded: "Instead of tough talk and no action, we need to do what Kennedy, Nixon and Reagan did and use all elements of American power — including tough, principled and direct diplomacy — to pressure countries like Iran and Syria. George Bush knows that I have never supported engagement with terrorists, and the president's extraordinary politicization of foreign policy and the politics of fear do nothing to secure the American people or our stalwart ally Israel."

The president asserted the United States has an unbreakable bond with Israel and suggested that those who think breaking it will create an advantage for the United States do not understand the nature of the threat.

"Some people suggest that if the United States would just break ties with Israel all our problems in the Middle East would go away," Bush said. "This is a tired argument that buys into the propaganda of the enemies of peace, and America utterly rejects it. Israel's population may be just over 7 million. But when you confront terror and evil, you are 307 million strong, because the United States of America stands with you."

He added that it's unthinkable that the strongest democracy in the Mideast is the one that receives the bulk of U.N. resolutions declaring violations of human rights.

"We believe that democracy is the only way to ensure human rights. So we consider it a source of shame that the United Nations routinely passes more human rights resolutions against the freest democracy in the Middle East than any other nation in the world," he said.

Prior to his speech, the president traveled to Masada, one of the Jews' last stands against Romans in the A.D. first century. Nearly 1,000 Jews committed suicide on the mountaintop after surviving three years staving off Roman conquerors who had destroyed the second temple in Jerusalem — the holiest site for Jews that is now covered by the Dome of the Rock Mosque — and eventually were able to figure a way up the mountain to kill the men and enslave the women there. The site is the place where Israeli soldiers take their oath to defend the Israeli state.

Bush's five-day Mideast journey, which was to take him to Saudi Arabia and Egypt, represents another effort to push Mideast peace talks forward as his time in office winds down. Israel and the Palestinians hope to reach an agreement before Bush leaves office next January.

Speaking before Bush, Israeli Prime Minister Ehud Olmert said his nation is committed to working with the U.S. and Palestinians on a lasting peace agreement — one laid out by Bush that envisions two independent states living side by side, which was the original objective of the United Nations when Israel was given statehood in 1948, days before war was declared on the nascent country by five of its Arab neighbors.

When a deal is reached, Olmert says the divided parliament and Israeli public will rally behind it.

"When the day comes for a historic peace agreement between us and our Palestinian neighbors, it will be brought to the approval of this house," Olmert said. "I am convinced: a peace agreement that will reflect the vision you presented to the world in June 2002 and that will be based on two states for two people, a Jewish state and a Palestinian state, living side by side in peace. This agreement will be approved in the Knesset by a large majority and will be supported by the vast majority of the Israeli public."

But while the president received a very warm welcome in the Knesset, not everyone there wanted to hear Olmert's message. The chamber reacted with silence and nervous laughter, then Bush began to laugh. Two hardline lawmakers walked out of the chamber in protest. As Bush began speaking, three lawmakers held up pieces of papers with the message, "We shall overcome." Security guards approached them and led them from the chamber.

Bush began his address by exclaiming in Hebrew, "Yom Atzmaut Sameach," or "Happy Independence Day." He spoke of Israeli history by noting generations of anti-Semitism and efforts to exterminate Jews. He said the United States will stand with the Israelis against terrorism and extremism. "We will never let down our guard or lose our resolve," he said.

The Associated Press contributed to this report.