A senior Israeli official said on Sunday the United States should not wait for Iran to decide on building a nuclear weapon before it considers military action against the Islamic Republic

"When is the point at which it should be stopped? Just when the bomb is assembled on the tip of the missile and is ready for launch?" Dan Meridor, deputy Israeli prime minister with responsibility for nuclear and intelligence affairs, said in a radio interview.

Prime Minister Benjamin Netanyahu, who sees a mortal threat to Israel from Tehran, has hinted he could resort to war unless Washington and other world powers give Iran an ultimatum on curbing its uranium enrichment programme.

U.S. President Barack Obama has rebuffed Netanyahu's lobbying, opening a rift between the allies although they agree that Iran has yet to take the final steps of purifying uranium to military grade and assembling a warhead.

Tehran denies seeking the bomb, saying its nuclear projects are for peaceful energy and medical purposes. Diplomatic talks between it and world powers have so-far proved fruitless.

Speaking on Israel Radio, Meridor praised the Obama administration for its insistence that it will not allow Iran to get nuclear arms. But such shows of resolve must be emphasized, he said.

Iran could reach stage of nuclear development which would allow it to make a warhead quickly years in the future when the world's guard was down, he said.

"This demands clarification, to my mind, to make clear that even an Iran that is a decision away from nuclear weaponry, be it within days or weeks, is a nuclear-armed Iran," Meridor said.

The Israelis have made clear they sees the window of opportunity to strike Iran closing as it digs in and defends its facilities.

While not explicitly stating when they would consider Iran close enough to the nuclear threshold to warrant a war, Israeli officials say they are watching the pace of its fortification, its uranium enrichment to 20 percent purity - just short of bomb-fuel grade, and its production of enrichment centrifuges.

"I think the question is when the crucial stage is passed beyond which you will be hard-pressed to stop Iran from assembling a nuclear bomb," Netanyahu said in a Jerusalem Post interview published on Sunday.

Israeli Defence Minister Ehud Barak accused Iran in May of pursuing a strategy that would allow it to build a bomb at 60 days' notice.

Israel refuses to confirm or deny its own nuclear capabilities, which are widely believed to include the Middle East's only atomic arsenal. Iran's eastern neighbor, U.S.-allied Pakistan, is also nuclear-armed.