Israel's Benjamin Netanyahu will argue for the need to set a "red line" for Iran's nuclear programme in his UN speech on Thursday, a confidant to the prime minister said, playing down differences with Washington.
Netanyahu faces the world body a day after U.S. President Barack Obama disappointed some Israelis by imposing no ultimatum to the Iranians in his own address, though he did warn that time for diplomacy with Tehran "is not unlimited".
Israel sees a mortal threat in a nuclear-armed Iran and has long threatened to strike its arch-foe pre-emptively, agitating war-wary world powers as they pursue sanctions and negotiations.
Complicating Netanyahu's strategy have been his testy relations with Obama as a U.S. election looms, and the reluctance of many Israelis to trigger an unprecedented conflict with Iran, which denies that it is seeking to develop nuclear weapons and has pledged wide-ranging retaliation if attacked.
"The prime minister has already presented red lines in the past. But we have yet to persuade the entire world to present those same red lines," Environment Minister Gilad Erdan, an influential member of Netanyahu's rightist Likud party, told Israel's Channel Two television.
He said Netanyahu, in his speech at the United Nations General Assembly, "will present them again, will explain why there is a danger not just to Israel, but to the whole West, to the United States, to the whole free world, should Iran pass a certain (nuclear) threshold".
Netanyahu has said that Iran could have enough low-enriched uranium by early 2013 to refine to a high level of fissile purity for a first nuclear device. Israel worries that this final step, if taken, could happen too quickly or quietly to be prevented.
Iran has said it has no plans to enrich uranium beyond the 20 percent purity required to run a reactor producing medical isotopes. That level, however, brings raw uranium exponentially closer to the 90 percent enrichment required for a bomb.
Though reputed to have the Middle East's sole nuclear arsenal, Israel's forces would be hard-put to deliver lasting damage to Iran's remote facilities and handle a multi-front war.
Locating a completed nuclear warhead in Iran, Erdan said, "would be almost impossible, whereas today we still know where the production facilities of that nuclear warhead are".
Netanyahu's public calls for a U.S. ultimatum have deepened acrimony with Obama, a Democrat accused by his Republican rivals of being soft on the Jewish state's security.
The Israeli prime minister denies meddling in the November presidential election in the United States, and Erdan shrugged off his spats with Obama.
"I have no intention of whitewashing and say there are no disagreements between Obama and Netanyahu. But it still doesn't mean anything. Even between a married couple there are sometimes difficult disagreements. It still doesn't mean the pact between them becomes less solid," Erdan said.
Netanyahu, who heads a broad-based, conservative coalition government, said he would take the U.N. podium for an Israel "united in the goal of preventing Iran from achieving nuclear weaponry".
But surveys show that most Israelis - apparently swayed by the open dissent of several senior national-security figures - would oppose launching unilateral strikes on Iran, given the risk of alienating Washington and of sparking knock-on clashes with Tehran's Islamist militant allies in Lebanon and Gaza.
A poll published by the liberal Haaretz newspaper on Thursday found that 50 percent of Israelis feared for the survival of their country, should there be a conflict.
Israeli opposition leader Shaul Mofaz criticised Netanyahu for sparring with Obama and voiced confidence in U.S. resolve.
"I am convinced that the United States, the president of the United States, is determined to prevent Iran going nuclear," Mofaz told Israel's Army Radio.
Even within Netanyahu's coalition there have been misgivings about the pitch of disagreement with the United States.
Danny Ayalon, deputy to Foreign Minister Avigdor Lieberman, described Obama's Iran remarks at the United Nations as "important, albeit measured".
Speaking on Israel Radio, Ayalon said the Netanyahu government and Obama administration were in discreet contacts and approaching agreement on setting limits for Iran.
"And the more Iran flouts the whole world, this coming together will, ultimately, reach a unanimity of positions and absolute similarity," he said.