Binyamin Netanyahu, the Israeli prime minister, said the only way to prevent Iran from acquiring nuclear weapons was by setting "a clear red line" to stop its atomic programme.
"At this late hour, there is only one way to peacefully prevent Iran from getting atomic bombs and that's by placing a
clear red line on Iran's nuclear weapons programme," Netanyahu said in a speech at the UN General Assembly on Thursday.
"Red lines don't lead to war; red lines prevent war."
'World's future at stake'
Mark Regev, spokesperson for the Israeli prime minister's office, told Al Jazeera
: "Do we just let the clock tick itself out? No, we establish a clear red line. That's the way to maintain the peace, and make war further distant."
He added: "Obviously in the framework for today with an extremely radical regime in Tehran ... It's not about Israel, as our Arab neighbours share our concerns."
During his speech, Netanyahu alleged Iran was already 70 per cent of the way through the process of enriching enough uranium to fuel a bomb, and must be prevented from reaching the 90 per cent level.
To illustrate his point, the Israeli leader used the world stage at the UN to present a cardboard diagram of a bomb with different levels on it, drawing a thick red line across it with a marker pen for dramatic effect.
"Faced with a clear red line Iran will back down," he said, insisting that imposing an ultimatum on Tehran would not provoke war but help prevent it.
Marwan Bishara, Al Jazeera's senior political analyst, said: "If I had a dollar for every time Iíve heard that 'time has run out on Iranís nuclear programme', Iíd probably be a millionaire by now. Weíve heard this for the last 25 years, itís just that itís not very credible."
Israel has warned that it could launch military action against Iran in order to prevent it reaching a certain nuclear threshold, and has urged the international community to force Tehran to abandon its atomic quest.
Iran denies it is building a nuclear weapon and has dismissed the Israeli threat.
Barack Obama, the US president, vowed in his address to the UN on Tuesday that he would prevent Iran from getting the bomb but his administration has repeatedly rejected imposing a red line on Tehran.
"At stake is the future of the world," Netanyahu said. "Nothing could imperil our future more than an Iran armed with nuclear weapons.
He recounted a long list of "terrorist" attacks which he blamed to Iran, and warned that "given this record of Iranian aggression without nuclear weapons, just imagine this aggression with nuclear weapons.
"If their terror networks armed with atomic bombs, who among you would feel safe in the Middle East? Who would be safe in Europe? Who would be safe in America? Who would be safe anywhere?" he asked.
And he warned that the international community could not rely on its own arsenals to deter Iranian aggression, denouncing Iranian leaders as religious fanatics who would be quite prepared to sacrifice their own population.
Most Israelis 'oppose unilateral strike'
With relations between Netanyahu and Obama already viewed as testy, US Defence Secretary Leon Panetta earlier this month highlighted the policy split further when he rejected Israel's "red lines" outright.
"The fact is, look, presidents of the US, prime ministers of Israel or any other country - leaders of these countries don't have, you know, a bunch of little red lines that determine their decisions," Panetta said.
"What they have are facts that are presented to them about what a country is up to, and then they weigh what kind of action is needed to be taken in order to deal with that situation," he told Foreign Policy magazine.
"I mean, that's the real world. Red lines are kind of political arguments that are used to try to put people in a corner."
Israel sees a mortal threat in a nuclear-armed Iran and has long threatened to strike its arch-foe pre-emptively, agitating war-weary world powers as they pursue sanctions and negotiations.
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 provoking clashes with Tehran's allies in Lebanon and Gaza.
Iran denies that it is seeking to develop nuclear weapons and has pledged wide-ranging retaliation if attacked.
"The prime minister will set a clear red line in his speech that will not contradict Obama's remarks. Obama said Iran won't have nuclear weapons. The prime minister will clarify the way in which Iran won't have nuclear arms," a senior Israeli official said prior to the speech.
Though he has not previously detailed when Israel might be willing to go to war, Netanyahu has said 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 per cent purity required to run a reactor producing medical isotopes. That level, however, brings raw uranium exponentially closer to the 90 per cent enrichment required for bomb fuel.
Though reputed to have the Middle East's sole nuclear arsenal, Israel would be hard-pressed to deliver lasting damage to Iran's remote facilities using its conventional forces, or to handle a multi-front war.
Mahmoud Ahmadinejad, the Iranian president, said in his speech to the General Assembly on Wednesday, said Iran was under threat of military action from "uncivilised Zionists," a clear reference to Israel. Earlier this week, Ahmadinejad said that Israel would eventually be "eliminated".
"In our endeavour we do not seek to delegitimise an existing state - that is Israel - but rather to assert the state that must be realised - that is Palestine"
The Israeli newspaper Haaretz
also ran excerpts from a leaked Foreign Ministry report that sanctions had caused greater damage to Iran's economy than anticipated by Israel.
The findings, confirmed to the Reuters news agency by an Israeli official, could undermine any attempt by Netanyahu to argue that the military alternative must be considered imminently.
Shortly before Netanyahu took to the podium, Mahmoud Abbas, the Palestinian president, asked the UN to grant Palestinians "non-member observer state" by the end of the year.
He told the General Assembly talks on such a status had begun, and that his eventual aim was to establish Palestine as a full member state.
"In our endeavour," he said, "we do not seek to delegitimise an existing state - that is Israel - but rather to assert the state that must be realised - that is Palestine."
Addressing the assembly later, Netanyahu accused Abbas of slandering his country.
"We won't solve our conflict with libelous speeches at the UN. We wont solve our conflict with unilateral declarations of statehood," Netanyahu declared, shortly after Abbas condemned Jewish settlement building as "racist".