But politicians' words and "intelligence leaks" sometimes seem designed to magnify the threat, providing Israel with a tool for swaying internal and US public opinion.
Fears are also voiced in tiny, oil-rich shiekhdoms to the south. "When Iran acquires nuclear weapons, it will blackmail all its neighbors," says Jamal al-Suwaidi, director of the Emirates Center for Strategic Studies and Research in Abu Dhabi. "It will put the whole Gulf under a cloud."
Iran's stated policy is to ensure peace in the region. And some argue that nuclear weapons could provide that stability.
"When Mao and Stalin acquired nuclear weapons, they calmed down," says Martin van Creveld, an Israeli military historian in Jerusalem. "If Islamic states get the bomb, the effect will be the same. Once you have the 'absolute weapon,' war ceases to be fun. It becomes suicide."
That lesson is not lost on Iran. Steven Zaloga, a senior missile analyst at the Virginia-based Teal Group, says: "Iran is not looking for war-fighting capability against Israel. It is looking to be able to inflict political damage...."
Determining the nature of Iran's nuclear effort isn't easy. The country is big enough to hide a major program, and internal politics are chaotic. "There could be two secret bomb programs, one run by the defense ministry and the other by the Revolutionary Guards," says a Western diplomat. "Each could be unknown to the other."
Iran has signed the Nuclear Non-Proliferation Treaty. But other indicators point to a 1970s nuclear program that was revitalized in the 1980s. Then-President Ali Khamenei said in 1987: "Regarding atomic energy, we need it now.... The least we can do ... is to let our enemies know that we can defend ourselves."
But progress has been slowed by a number of factors: