Israel's Prime Minister on Monday vigorously asserted his country's right to defend itself against the nuclear threat emanating from Iran, warning that time was growing short and declaring he wouldn't 'gamble with the security of the state of Israel'.

Benjamin Netanyahu's tough talk in a speech to thousands of American Jewish supporters was his strongest suggestion yet that he wouldn't hesitate to launch a unilateral pre-emptive attack on Iran. It differed starkly in tone from President Barack Obama's appeal earlier in the day to give diplomacy and sanctions more time to work before resorting to force.

Israel has 'patiently waited' for diplomacy and sanctions to work but time is working against that approach, Netanyahu told a record gathering of the America Israel Public Affairs Committee, the pro-Israel lobby in Washington.

"None of us can afford to wait much longer. As Prime Minister of Israel, I will never let my people live in the shadow of annihilation," he said to a roaring standing ovation.

Israel, like the U.S. and much of the West, rejects Iran's claims that its nuclear program is designed to produce energy and medical isotopes. The head of the U.N. nuclear agency fed concerns further on Monday by saying his organization had 'serious concerns' that Iran may be hiding secret atomic weapons work.

But Israel and the U.S. disagree over when a strike might be appropriate and how effective a unilateral Israeli attack might be against scattered and heavily fortified Iranian nuclear facilities.

The Israeli leader dismissed arguments that an attack on Iran would exact too heavy a toll by provoking Iranian retaliation. He held up a copy of a 1944 letter from the U.S. War Department rejecting world Jewish leaders' entreaties to bomb the Auschwitz death camp because it would be 'ineffective' and 'might provoke even more vindictive action by the Germans'.

"My friends, 2012 is not 1944," Netanyahu said. "Today, we have a state of our own. And the purpose of the Jewish state is to defend Jewish lives and to secure the Jewish future."

Netanyahu's speech drew tumultuous applause and numerous standing ovations from the crowd of more than 13,000 people, reflecting the immense support Israel enjoys in the U.S.

It also drew attention to the gap between the U.S. and Israel over how to handle Iran.

As he entered his meeting with Netanyahu at the White House earlier on Monday, Obama declared, "The United States will always have Israel's back," but quickly added, that "both the prime minister and I prefer to solve this diplomatically."

Netanyahu responded that Israel must remain 'the master of its fate' but made no reference to letting diplomacy and sanctions percolate.

Israel assesses that Iran is close to being able to build a bomb and wants to stop it before it reaches that point. Some Israeli defense officials have said Israel must strike by summer because Iran is moving key operations out of the reach of Israeli air power.

The Obama administration sees this course as dangerously premature, arguing that Tehran has not yet decided whether to actually produce atomic weapons and might still respond to non-military pressure. Because of its superior firepower, the U.S. reasons it would be able to act many months after Israel could.