PAUL KENYON: None at the U.N.'s team in Iran has ever before spoken publicly, but Chris Charlier she tells me about the difficulties of inspecting here.
CHRIS CHARLIER: Whatever we say, whatever we do, they are always behind us with a video camera, with a microphone trying to record things that we saying. And it's a little disturbing because some people don't like it. You know, usually when we work, we don't like to have always somebody behind us, behind our shoulders and looking what we're doing or recording what we're saying. But, you know, it's part of the game.
PAUL KENYON: Charlier and his colleagues have been traveling the country checking out nuclear sites that until recently the world didn't know existed. The inspectors take samples and test particles, and report back their findings to the headquarters in Vienna. As a site called Lavizan, on the outskirts of Tehran, the U.N. suspected a nuclear facility. But the Iranians wouldn't let them in.
CHRIS CHARLIER: When we asked them to get access there, they started, you know, "Well, there's nothing there," you know. "We just dismantled building, and there was nothing related to agency activities." And finally, after months of discussion, we went there.
PAUL KENYON: When they finally got access, Lavizan had changed from this to this. It had been dismantled, bulldozed over, leaving nothing behind. Until recently, Iran's most closely guarded secret was the uranium enrichment facility six hours south of Tehran, called Natanz. We decide to head there ourselves, across a desolate plain protected by mountains. Natanz has never been filmed before.
This uranium enrichment facility is the size of six football fields, and it's almost entirely underground. As you get closer, you see anti-aircraft positions. The Iranians have covered Natanz with thick layers of concrete and steel to keep it safe from the bunker-busting bombs that Iran fears the United States or Israel will use against it. Iran's pattern of behavior around Natanz and the other sites is deeply concerning to the UN inspectors.
CHRIS CHARLIER: They tried, really, I believe, to conceal their program and the activities. And, yeah, well, maybe there is things -- still others things that they are doing and we couldn't find, and that's why we are getting suspicious.
PAUL KENYON: We catch up with the inspection team at a hotel near Natanz. They've just come from a nuclear facility there. Part of the inspector's job is to install surveillance cameras to make sure the Iranians aren't doing anything undeclared.
I want to know the latest data from the camera at Natanz, but inspector Daniel Baudinet is wary about talking. He says the security services have just been called about us, and he isn't comfortable being filmed.
DANIEL BAUDINET: This is the guy from the facility.
PAUL KENYON: Oh, is he?
DANIEL BAUDINET: Yes.
PAUL KENYON: Yeah. Did he look angry? Is he going to stay? Is he coming in now?
DANIEL BAUDINET: No, no, no, no, no. But he was phoning now. As soon as he saw you, he phoned.
PAUL KENYON: We know we're being followed, as we head south toward the ancient city of Esfahan. On the banks of the Zayandeh River, Isfahan is a popular holiday destination for Iranians. The inspectors have come here to monitor another major nuclear facility. The next morning, we head out with the inspectors to a nuclear facility near Isfahan. Anti-aircraft positions tell us we're close.
Here, uranium arrives as yellowcake, and leaves in tanker trucks ready for enrichment 100 mile as way at Natanz. The Iranians say this is all for their nuclear energy program. But the problem is, once they have the complete nuclear fuel cycle, they're not far from the material to make weapons. The next morning, the UN team sets off for another inspection. The security services tell us we'll be arrested if we follow them. Then we're told to leave the area. They send us the long way back to Tehran, to keep us from taking more pictures of nuclear sites.
But once back in the capital, we go looking for another. The Iranians have hidden it among the warehouses of East Tehran. It's called the Kalaye Electric Company. It used to be a clock factory, but now the UN believes it's where Iran has been conducting nuclear experiments. The inspectors wanted to test for nuclear particles, but the Iranians seem to have attempted a cover-up.
CHRIS CHARLIER: You know, the building was a little bit suspicious. Everything was just brand new. It was even still smelling the painting, you know, because it was just freshly painted. So, you know, I think the activities which was going there, they had something to hide, and they renovated the building before we arrived.
PAUL KENYON: We wanted to talk to the Iranians about the nuclear sites we've seen. But at Tehran University, we find this man, Ali Akbar al-Salehi. He's a professor now. But, until recently, he was Iran's top nuclear negotiator. When the UN first learned about Iran's secret nuclear program, Salehi defended to it the world. He's still defending it now.
ALI AKBARA AL-SALEHI: We are really not after nuclear weapons. We are not ashamed of saying it. I mean, we are not timid to say -- we are not a country to be timid of saying things that we wish to say or we wish to have. And we would have said it loudly if we wanted to go after nuclear bombs and nuclear weapons.
PAUL KENYON: Salehi insists Iran's nuclear program is peaceful. I ask: Why then was the site like the Kalaye Electric Company scrubbed and renovated before the U.N. inspectors arrived?
ALI AKBARA AL-SALEHI: Well, this is again a technical issue. I mean, people who are in this area, I mean, you cannot wash a room that you have done experiments, nuclear experiments, within. It's very easy to trace even the least amount of material in a room.
PAUL KENYON: Salehi's arguments are often technical and legal. But I press him on why they hid key parts of their energy program for nearly 20 years, and why the deception.
ALI AKBARA AL-SALEHI: You keep on saying "deceiving." I keep on saying that we were -- I mean, had we deceived the world, we wouldn't have been in this position.
PAUL KENYON: Why were you less than honest or less than forthright?
ALI AKBARA AL-SAEHI: Because of the sanction, international sanctions.
PAUL KENYON: When Salehi says "sanctions," he's referring to the U.S.-led trade embargo imposed after the hostage standoff at the U.S. Embassy here in 1979. Iran says those trade restrictions meant they couldn't buy a nuclear energy program openly, so they turned to the black market.
Iran is rich in oil, but they say they still need nuclear power to meet the energy demands of a population now grown to almost 70 million.