The U.N.'s nuclear agency is expected to report later this week that Iran is on the threshold of being able to build a nuclear bomb.
CBS News correspondent David Martin reports that the International Atomic Energy Agency will reveal new evidence that Iran is not just enriching uranium, but developing the capability to use it in a weapon.
Among other things, a satellite photo of an Iranian military base shows an enormous steel container apparently used to secretly test the high explosives needed to trigger a nuclear weapon.
"It's part of the evidence that's accumulating that Iran has continued to work on furthering its ability to make the nuclear weapon itself," said former U.N. weapons inspector David Albright, who has seen much of the evidence.
"They know how to make a crude or a nuclear weapon that they could test underground," said Albright, adding that they don't quite have a weapon they could use against their enemies.
The IAEA assessment scheduled to be released later this week contains evidence Iran has been working on computer models of a warhead small enough to be launched by a missile that could reach Israel and much of Europe.
"Some of the evidence suggests that they're within a year of that. Other evidence suggests that they're four years away," Albright said.
Despite diplomatic pressure, economic sanctions, covert sabotage and threats of military action, Iran appears to be slowly closing in on a nuclear weapon.