In a speech to 16,000 members of AIPAC, America's largest pro-Israel lobby group, that had the air of a political rally early on Monday, Mr Netanyahu said that he meant no disrespect to Mr Obama, but insisted a negotiated settlement with Iran over its nuclear program would pose an existential threat to Israel.

Later Mr Obama told Reuters that while he had no personal issue with Mr Netanyahu, the US had its own policymaking process, adding that Mr Netanyahu's warnings over preliminary agreements with Iran had proved unfounded.

Mr Netanyahu believes the US should lead increased world sanctions to force Iran to give up its program. Mr Obama believes that only a negotiated settlement leaving Iran some peaceful nuclear capacity can ensure Iran does not pursue its weapons program in secret.

Mr Obama has made it clear he considers a settlement with Iran to be a top priority of the White House. The President left it to National Security Adviser Susan Rice to explain in detail to the AIPAC conference why Mr Obama believes his path is surer.

At times the crowd's cheers for Dr Rice's address veered close to jeers. "I know some would argue we should impose sanctions and just walk away, but let's remember -  " she said, prompting overwhelming applause that forced her to pause before going on to say " - my friends, let's remember that sanctions have never stopped Iran from advancing its program."

She warned against Israel demanding "unreasonable and unachievable outcomes" with Iran, saying that "no one can make Iran unlearn the scientific and nuclear expertise it already possesses".

"If we insist on no enrichment, our partners will abandon us. Simply put, that is not a viable nor obtainable negotiating position," Dr Rice said.

In his interview with Reuters Mr Obama said again that the US would accept no deal before a bad deal, and that any deal would include a 12-month "breakout point". That is, Iran's technology would be withheld to the point where it needed at least a year to develop a bomb from the moment it broke agreements, giving the international community time to either reintroduce sanctions or mount a military assault.

During his speech to AIPAC, Mr Netanyahu said that while US leaders were concerned for American safety, Israel's were forced to fear for their nation's very survival, and this perspective had lead to disagreements between the two nations in the past. But he said the relationship – more like family than friends – had survived and grown stronger.

Though Mr Obama agreed – at least to the point of saying that the discord between the leaders is not "permanently destructive" – observers agree that Mr Netanyahu's speech has caused real damage to the relationship between the nations.

The decision by the House Speaker, the Republican John Boehner, to extend an invitation to Mr Netanyahu to address a joint session of Congress has been described as everything from a serious breach of protocol to a breach of the Constitution, which grants responsibility for foreign affairs solely to the president.

Mr Netanyahu's decision to accept the invitation has provoked anger in both the US and Israel. Some have suggested that Mr Netanyahu, running for re-election in a fortnight, has risked angering his nation's key ally for domestic political gain.

Around 30 Democrats, including US Vice-President Joe Biden, who also serves as the president of Senate, have decided not to attend Mr Netanyahu's speech on Tuesday morning in Washington, DC.

The fallout has been significant and even ugly at times. Last week Dr Rice told an interviewer: "What has happened over the last several weeks — by virtue of the invitation that was issued by the Speaker and the acceptance of it by Prime Minister Netanyahu two weeks in advance of his election — is that on both sides, there has now been injected a degree of partisanship.

"It's destructive of the fabric of the relationship."

In response over the weekend, the controversial reality TV figure and failed Republican candidate Rabbi Shmuley Boteach took out a full-page advertisement depicting Dr Rice surrounded by skulls and declaring she was blind to genocide.

American Jewish groups almost unanimously condemned the ad, calling it "revolting", "grotesque" and a "sinister slur". Marshall Wittman, a spokesman for AIPAC, said: "Ad hominem attacks should have no place in our discourse."

But one conservative US radio host said those members of Congress who have decided not to attend should be hanged in front of the Capitol.

"I would like to think that these guys could pay with their lives, hanging from a noose in front of the US Capitol building," said Andrea Shea King. "Most of those members who are opting out of attending the speech are members of the Congressional Black Caucus. And their districts are all dumb clucks. Because the dumb clucks wouldn't be electing these people if they knew better."