Israeli Prime Minister Benjamin Netanyahu warned on Sunday that Iran was just six to seven months away from being able to build a nuclear bomb, adding urgency to his demand that President Barack Obama set a clear "red line" for Tehran in what could deepen the worst US-Israeli rift in decades.

Taking to the television airwaves to make his case directly to the American public, Netanyahu said that by mid-2013, Iran would be 90 per cent of the way toward enough enriched uranium for a bomb.

He urged the US to spell out limits that Tehran must not cross if it is to avoid military action - something Obama has refused to do.

"You have to place that red line before them now, before it's too late," Netanyahu told NBC's "Meet the Press" program, saying that such a US move could reduce the chances of having to attack Iran's nuclear sites.

The unusually public dispute - coupled with Obama's decision not to meet with Netanyahu later this month - has exposed a deep US-Israeli divide and stepped up pressure on the US leader in the final stretch of a tight presidential election campaign.

It was the clearest marker Netanyahu has laid down so far on why he has become so strident in his push for Washington to confront Tehran with a strict ultimatum. At the same time, his approach seemed certain to stoke further tensions with Obama, with whom he has had a notoriously testy relationship.

Senior US officials say Iran has yet to decide on a nuclear "breakout" - a final rush to assemble all the components for a bomb - and they express high confidence that Iran is still at least a year away from achieving the capacity to build a bomb if it wanted to.

This contrasts with Netanyahu's timetable, although the Israeli leader stopped short of saying Iran had decided to manufacture a weapon.

Netanyahu showed no signs of backing down on Sunday and even sought to equate the danger of a nuclear-armed Iran with the Islamist fury that fueled attacks on US embassies across the Muslim world last week and shocked many Americans.

"It's the same fanaticism that you see storming your embassies today. You want these fanatics to have nuclear weapons?" Netanyahu asked in the NBC interview, in a clear emotional appeal to Americans still reeling from the angry protests sparked by a film that mocked the Prophet Mohammad.

There have been no accusations, however, of any Iranian role in stoking the violence that have swept Muslim capitals from the Middle East to Africa in the past week.

Netanyahu said a strong ultimatum was needed to Iran, which denies it is seeking a nuclear bomb. "They're in the 'red zone'," Netanyahu said, using a colorful American football metaphor that describes when a team is close to scoring a touchdown.

"They're in the last 20 yards. And you can't let them cross that goal line," he said. "Because that would have unbelievable consequences."

Asked whether Israel was closer to acting on its own despite Obama's call for more time for sanctions and diplomacy to work, Netanyahu said: "We always reserve the right to act. But I think that if we are able to coordinate together a common position, we increase the chances that neither one of us will have to act."

Obama, seeking re-election in November, has faced harsh criticism from Republican presidential rival Mitt Romney, who has seized on US-Israeli differences to accuse the Democratic president of being too tough with Israel and not tough enough with Iran.

Netanyahu's sharpened rhetoric in recent days had stoked speculation that Israel might attack Iran before the US ballot, believing that Obama would give it military help and not risk alienating pro-Israeli voters.

But Netanyahu has drawn criticism at home for overplaying his hand, and he faces divisions within the Israeli public and his own government that will make it hard to launch a unilateral strike any time soon.

Possibly seeking to soften the edge with Washington, Netanyahu said he appreciated the president's assurances that Iran would not be allowed to obtain a nuclear weapon.

"I think implicit in that is that, if you're determined to prevent Iran from getting nuclear weapons, it means you'll act before they get nuclear weapons," he said.

But Netanyahu, whose persistent "red line" demands have infuriated US officials, again made clear that was not enough.

"It's important to communicate to Iran that there's a line that they won't cross," he said. "I think a red line, in this case, works to reduce the chances of the need for military action. Because once the Iranians understand that there's a line that they can't cross, they're not likely to cross it."

Drawing a parallel not likely to go down well with the Obama administration, Netanyahu said that if the United States had set a red line before Iraqi leader Saddam Hussein invaded Kuwait in 1990, "maybe that war could have been avoided."

In his most specific comments to date on the subject, Netanyahu told CNN: "They're moving very rapidly to completing the enrichment of the uranium that they need to produce a nuclear bomb. In six months or so they'll be 90 per cent of the way there."

He appeared to be referring to Iran's enrichment of uranium to 20 per cent purity, a level it says is required for medical isotopes but which is also close to bomb-fuel grade. According to an August report by UN inspectors, Iran has stockpiled 91.4 kg of the 20 per cent material.

Experts say around 200-250 kg would be the minimum required to enrich further into enough material for a bomb, a threshold Iran could potentially reach soon by producing roughly 15 kg a month, a rate that could be speeded up if it activates new uranium centrifuges.

Israeli Defense Minister Ehud Barack has warned that Iran may be approaching a "zone of immunity" in which Israeli bombs would be unable to penetrate deeply buried uranium enrichment facilities.

The US has more potent weapons that would allow more time for the sanctions push to work. Israel is widely believed to possess the Middle East's only nuclear arsenal.-Reuters