BARACK Obama vowed he would "not hesitate to use force" to prevent an Iranian nuclear weapon on Sunday, but chided Israel for its "loose talk" of impending war and demanded more time for a diplomatic solution.
Speaking before a critical White House showdown Monday with Benjamin Netanyahu, Israel's prime minister, Mr Obama tried to buy more time for "crippling sanctions" against Tehran to take effect before Israel decides to strike its nuclear facilities.
"Iran's leaders should know that I do not have a policy of containment," Mr Obama told a major pro-Israeli conference in Washington. "I have a policy to prevent Iran from obtaining a nuclear weapon".
Stressing that a nuclear-armed Iran also threatened American security, he added: "I will not hesitate to use force when it is necessary to defend the United States and its interests".
However, he urged Israeli leaders to "let our increased pressure sink in", emphasising: "Now is not the time for bluster" and citing Theodore Roosevelt's dictum to "speak softly, but carry a big stick".
"There is too much loose talk of war," Mr Obama said. "Such talk has only benefited the Iranian government, by driving up the price of oil, which they depend upon to fund their nuclear programme."
Mr Obama received enthusiastic applause from the audience, which organisers claimed numbered 13,000, when stressing his threat of military action and paying tribute to the strength of US-Israeli ties. However his appeal to halt the drumbeat of war met total silence.
Mr Obama, who has repeatedly faced accusations of coolness to the US-Israeli alliance, told thousands of activists gathered for the AIPAC conference: "When the chips are down, I have Israel's back".
With his potential Republican opponents falling over each other to appear more pro-Israeli, he repeatedly sought to revive his support among Jewish voters, which has dropped since 2008.
Yet as he prepared to face demands from Mr Netanyahu for "red lines" that would trigger US action if crossed by Iran, he stressed that current assessments were that Iran had no weapon. "In 2012, the Iranian government faces the prospect of even more crippling sanctions," he added.
Mr Obama was praised by Shimon Peres, Israel's president, who told the conference he was "leading and implementing an international, complex and decisive policy" towards the crisis.
"There is no space between us," Mr Peres claimed of the US-Israel approach to the crisis. "Iran will not develop a nuclear weapon." His enthusiastic endorsement appeared to be an attempt to thaw the frosty relationship between Mr Obama and Mr Netanyahu, who is frustrated with mixed messages emerging from Washington. Israeli officials have indicated their uncertainty of Mr Obama's commitment may force their own strike on Iran this year.
Avigdor Lieberman, Israel's foreign minister, Sunday said American pressure would not affect Israeli thinking. "We are an independent sovereign state, and at the end of the day, the state of Israel will make the most correct decisions as we understand them," he said.
Israeli government sources suggested that in his own speech to AIPAC today, Mr Netanyahu would take a much harder line and "break new ground" in his remarks about Iran.
Mr Obama has toughened his rhetoric in the approach to their summit, telling an interviewer last week: "When I say that a situation in which Iran has nuclear weapons is something that is unacceptable, I meant it, I don't bluff." Former senior officials from the George W. Bush administration said Mr Obama should be taking a more aggressive stance.
Elliott Abrams, a senior White House aide to Mr Bush, said he believed Mr Obama's current stance was failing to dissuade the Israeli administration from attacking. "I just don't think it's going to do it," Mr Abrams told The Daily Telegraph. "They want a clearer statement that the US would absolutely prevent Iran from getting a nuclear weapon.
Mr Abrams said "high-ranking Arab diplomats" were telling him that the US might as well attack before Israel does. "They say 'you're going to get blamed anyway if Israel strikes, because people will think you were complicit. The difference is that you'll do it a lot better – so do it'," he said.
• North Korea may have exploded an Iranian nuclear bomb in 2010 in a secret test, a German defence expert has claimed.
In an article published in the newspaper Welt am Sonntag, Hans Ruhle, a former German defence ministry official, cited evidence of two small nuclear tests in April and May 2010, and argued that one of them was for a “foreign entity, in this case Iran”.
The claim contradicts analysis from both Israeli and American intelligence that says Iran is not developing nuclear weapons, and, if true, could shift the balance of power in the Middle East.