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As allies closely monitor Iran's movements toward becoming a member of the nuclear club, President Obama assured Israel's leader on Monday that the United States "will always have Israel's back" even while pursuing a "window that allows for a diplomatic resolution."

Meeting at the White House a day after Obama addressed the nation's top Israel lobby, the American-Israel Public Affairs Committee, the two agreed that diplomacy is the best route for now although Benjamin Netanyahu stressed that his nation reserves the right to defend itself.

"When I say all options are on the table I mean it. Having said that I know both the prime minister and I prefer to solve this diplomatically," Obama said. The U.S. will consider all options in confronting what it sees as the unacceptable outcome of an Iranian bomb, he added.

"We do not want to see a nuclear arms race in one of the most volatile regions in the world. We do not want the possibility of a nuclear weapon falling into the hands of terrorists. And we do not want a regime that has been a state sponsor of terrorism being able to feel that it can act even more aggressively or with impunity as a consequence of its nuclear power," Obama said.

While the prime minister offered gratitude, he insisted Israel will be the "master of its fate."

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    "Israel must have the ability always to defend itself, by itself, against any threat," Netanyahu said, echoing the president's remarks to Sunday's annual conference.

    "When it comes to Israel's security, Israel has the right -- a sovereign right to make its own decisions. I believe that's why you appreciate, Mr. President, that Israel must reserve the right to defend itself. And after all, that's the very purpose of the Jewish state: to restore to the Jewish people control over our destiny," Netanyahu said.

    The two meet as a growing sense of urgency emerges in Israel that Iran is close to obtaining a long-sought nuclear weapon. Iran insists that its nuclear efforts are for peaceful purposes only, even as it threatens to blow Israel off the map.

    Obama is trying to avert an Israeli strike that could come this spring, and which the United States sees as dangerously premature. U.S. officials believe that while Tehran has the capability to build a nuclear weapon, it has not yet decided to do so.

    The president was expected to tell Netanyahu in private at the White House that although the U.S. is committed to Israel's security it does not want to be dragged into another war. Obama is unlikely to spell out U.S. "red lines" that would trigger a military response, despite Israeli -- and some congressional -- pressure to do so.

    The U.S. has won international sanctions on Iran in the United Nations and pledges that more are on the way. But that approach leaves Israel in a precarious spot. If Iran moves underground, literally, the Jewish state will lose its opportunity to shut down the facilities before the weapons are developed.

    Netanyahu has not publicly backed a military strike, but his government spurned arguments from top U.S. national security leaders that a preemptive attack would fail.

    Netanyahu suggested Monday that failure to prevent Iran from achieving weapons is as problematic for the U.S. as it is for Israel.

    "You know, for them, you're the Great Satan, we're the Little Satan. For them, we are you and you are us. And you know something, Mr. President? At least on this last point I think they're right: We are you and you are us; we're together," he said.

    The top U.S. military officer recently called a unilateral strike "imprudent," a mild catchall for the chain-reaction of oil price hikes, Iranian retaliation, terror strikes and a possible wider Mideast war that U.S. officials fear could flow from an Israeli strike.

    In citing the need to stop Iran, Israel points to the potential for the Islamic Republic to pass its weapons to terror groups like Hezbollah and Hamas, which already use ballistic missiles to strike Israel's population centers near the borders. Israel also fears a nuclear Iran would touch off an atomic weapons race in a region hostile to Israel's existence.

    The head of the U.N. nuclear agency said Monday his organization has "serious concerns" that Iran may be hiding secret atomic weapons work, as he acknowledged failure in his latest attempt to probe such suspicions and listed recent atomic advances by Iran.

    "The agency continues to have serious concerns regarding possible military dimensions to Iran's nuclear program," International Atomic Energy Agency chief Yukiya Amano said in Vienna.

    The Associated Press contributed to this report.