Two years? One? Even less?

Opinions differ on how close Iran may be to being able to develop a nuclear weapon, but concerned governments and experts agree the time to stop Tehran is growing short — and the options limited.

The time frame is increasingly important because of the possibility that Israel or the U.S. might opt to strike the Islamic Republic if they judge that all diplomatic options to end its nuclear defiance have been exhausted.

And with Tehran showing no signs of giving up uranium enrichment or heeding other international demands, the diplomatic window is growing increasingly narrow. That fact gives special significance to a meeting of the 35-nation board of the International Atomic Energy Agency and its chief focus of what to do about Iran.

Hard-line Iranian President Mahmoud Ahmadinejad appeared to stoke the flames Sunday, declaring that Iran's military will "break the hand" of anyone targeting his country's nuclear facilities.

He spoke during a military parade displaying various types of Iranian-made missiles. Also in the parade was a military truck carrying a huge banner saying "Israel should be eliminated from the universe" in both English and Farsi.

Iran insists its nuclear activities are geared only toward generating power. But Israel says the Islamic Republic could have enough nuclear material to make its first bomb within a year. The U.S. estimates Tehran's is at least two years away from that stage.

At the low end is physicist and former U.N. nuclear inspector David Albright. He says Tehran could reach weapons capacity in as little as 6 months through uranium enrichment.

An IAEA report drawn up for the IAEA board meeting says that Tehran has increased the number of centrifuges used to process uranium to nearly 4,000 from 3,000 just a few months ago.

But Albright, whose Washington-based Institute for Science and International Security closely tracks suspect secret proliferators, has also been able to extrapolate other information from the report that is less obvious but of at least equal concern.

Iran, he says, has managed to iron out most of the bugs in the intensely complicated process of enrichment that often saw the centrifuges breaking down. The machines, he says "now appear to be running at approximately 85 percent of their stated target capacity, a significant increase over previous rates."

That, he says means, they can produce more enriched uranium faster. And while the IAEA says that the machines have spewed out only low enriched material suitable solely for nuclear fuel, producing enough of that can make it easy to "break out" quickly by reprocessing it to weapons- grade uranium suitable for the fissile core of warhead.

To date, Iran has produced nearly 500 kilograms — about 1,000 pounds — of low enriched uranium, said the report — close to what Albright says is the 1,500-pound minimum needed to produce the 45-60 pounds needed for a simple nuclear bomb under optimal conditions.

And with Iran's centrifuges running ever more smoothly, it "is progressing toward this capability and can be expected to reach it in six months to two years," says Albright.

Additional work — making a crude bomb to contain the uranium — would take no more than a "several months," he said.

But that work could be done secretly and consecutively with the last stages of weapons-grade enrichment. With Iran limiting access of IAEA inspectors to facilities it has declared to the agency, the U.N. nuclear monitor is blind-sided in efforts to establish whether such covert atomic work is going on.

Iran insists it is an innocent victim of U.S. pressure. But international concern has grown enough to result in 3 sets of U.N. Security Council sanctions over the past two years. And Iranian stonewalling of IAEA inspectors probing allegations that it actively tried to modify a missile to carry a nuclear payload and conducted other weapons-related research has added to fears.

The IAEA report prepared for the board meeting that starts Monday faulted Iran for blocking efforts to further investigate the allegations, based on intelligence from the U.S. and several other IAEA member nations.

Part of the report spoke of what appeared to be drawings and calculations by Iranian engineers on reconfiguring its Shahab-3 missile to be able to carry a nuclear payload.

Iranian officials say the missile has a range of 1,250 miles, enabling a strike on Israel and most of the Middle East.

Such report stoke Israeli fears — and may force the Jewish state's hand.

Beyond veiled warnings from Israeli leaders of a possible last-resort strike, the country is building its capacities with weapons that could spearhead such action.

It has purchased 90 F-16I fighter planes that can carry enough fuel to reach Iran, and will receive 11 more by the end of next year. It has bought two new Dolphin submarines from Germany reportedly capable of firing nuclear-armed warheads — in addition to the three it already has.

And this summer it carried out air maneuvers in the Mediterranean that touched off an international debate over whether they were a "dress rehearsal" for an imminent attack, a stern warning to Iran or a just a way to get allies to step up the pressure on Tehran to stop building nukes.

Former Israeli Deputy Defense Minister Ephraim Sneh told the AP Sunday that "the military option for Israel is the last resort."

Still, those now in power leave no doubt that it remains on the table.

"If Israeli, U.S., or European intelligence gets proof that Iran has succeeded in developing nuclear weapons technology, then Israel will respond in a manner reflecting the existential threat posed by such a weapon," said Israeli Deputy Prime Minister Shaul Mofaz recently.

"Israel takes Mahmoud Ahmadinejad's statements regarding its destruction seriously."