With the most substantive talks in years underway between Tehran and Western powers, analysts are looking at what is generally known about Iran’s nuclear capability while warning that much of it remains secret.
The so-called P5+1 group of nations - the United States, Britain, France, China, Russia and Germany - are evaluating a proposal made by Iran during recent negotiations on Tehran’s suspected nuclear weapons program.
More talks are scheduled for early November in Geneva.
For years, the international community has been trying to persuade Iran to end its uranium enrichment program - but to no avail. Low enriched uranium can be used for civilian nuclear power plants, but highly-enriched uranium is an integral part of a nuclear bomb.
The United States and the European Union believe Iran is seeking to develop nuclear weapons, but Tehran says its program is for peaceful, civilian purposes.
Joel Rubin, Iran expert with the Ploughshares Fund, a foundation specializing in nuclear weapons policy, said that Western intelligence agencies know some details about Iran’s nuclear program.
“And that basically means that Iran is enriching uranium, that it does have 19,000 centrifuges spinning, that it is enriching uranium at a couple of key sites and that it has a stockpile of medium-enriched uranium near 20 percent that is less than what would take to construct enough fissile material for one bomb," he said. "And that they continue to develop this program."
Rubin said Iran is also building a plant that will produce plutonium, which can also be used in a nuclear weapon.
Much not known
Still, John Bolton, former U.S. ambassador to the United Nations, said too much remains secret about Iran's ambitions.
"I’m worried that there is a lot we don’t know - that the Iranians, perhaps with some tactical assistance from the North Koreans, who are expert at building things underground, have engaged in that kind of camouflage for a protracted period of time," he said. "So that there may be a lot more to the nuclear weapons program than we know about."
In an effort to pressure Iran to end its uranium enrichment program, over the past few years, the United Nations Security Council has passed resolutions imposing sanctions on Iran.
In addition, several other nations, including the United States, have imposed their own measures. And Israel has warned it will not stand by and watch Iran develop nuclear weapons. It is warning the West to tread cautiously in talks with Tehran.
Over the years, negotiations between Western nations and Iran have made little progress.
But analysts say this may change, following the June election of President Hassan Rouhani as Iran’s president - a man considered to be a moderate and who ran on a platform of diplomatic engagement with the West.
Initial talks positive
At a meeting in Geneva earlier this month, Western officials and Iran held negotiations described by Catherine Ashton, the European Union foreign policy chief, as “the most detailed talks we have ever had.”
At that session, Iran offered a proposal.
Daryl Kimball, head of the Arms Control Association, a private research firm, said the details of the Iranian offer remain confidential.
“And I think that’s a good sign, because it shows that each is not trying to use leaks in order to make rhetorical points, to score points back home," he said. "They are really trying to achieve an outcome.”
Experts say the Iranian proposal probably contains concrete steps Iran is willing to take - such as curtailing its uranium enrichment program - in exchange for easing Western economic and financial sanctions.
But analysts, such as the Ploughshares's Rubin, say that before any significant progress is made, both sides have to overcome a high level of mistrust.
“There’s more than three decades of mistrust and of concern between the sides. The United States designates Iran as a state sponsor of terrorism," he said. "They have an atrocious human rights record inside Iran. There are regional tensions and conflicts between Iran and Israel and the Gulf States and about Syria and other issues. So there are multiple layers here.”