Iran already has enough low-enriched uranium for several atomic bombs if refined to a high degree but it may still be a few years away from being able to build a nuclear-armed missile if it decided to go down that path.

Israel’s warning last week that Iran will be on the brink of developing a nuclear weapon by mid-2013 seemed to refer to when it could have a sufficient stock of higher-grade uranium to make a quick dash to produce a bomb’s worth of weapon-grade material.

But, analysts say, Tehran would need time also for the technologically complicated task of fashioning highly refined uranium gas into a nuclear warhead small enough to fit on a missile - if it opts for such weapons of mass destruction.

“If they haven’t worked out all the steps with dummy materials beforehand they will have a lot to do,” said a Vienna-based diplomat who is not from one of the six world powers involved in diplomacy over Iran’s disputed nuclear activity.

“Maybe they have all of the equipment ready. Maybe they have played with surrogate materials. I don’t think anyone knows.”

Experts stress that timeline estimates are fraught with uncertainty as it is unclear how advanced the Islamic Republic may be in its suspected nuclear bomb research.

“I still think that we are talking about several years ... before Iran could develop a nuclear weapon and certainly before they could have a deliverable nuclear weapon,” said Shannon Kile, head of the Nuclear Weapons Project of the Stockholm International Peace Research Institute, a think-tank.

Iran rejects suspicions of a covert quest for atomic bomb capability. But its refusal to curb nuclear work with both civilian and military applications, and its lack of openness with U.N. inspectors, have drawn tough Western sanctions.

A high-level group of U.S. security experts - including former national security adviser Zbigniew Brzezinski and former Deputy Secretary of State Richard Armitage - estimated that Iran would need between one and four months to produce enough weapons-grade uranium for a single nuclear device.