Satellite photos of two locations in Iran show the nation may be continuing to pursue and hide a program to produce nuclear weapons, images obtained exclusively by Fox News show.

One site at Natanz appears to show a hidden uranium enrichment plant, possibly surrounded by defense fortifications capable of thwarting an attack. The other site, Arak, is a heavy water facility used to make plutonium.

The two sites together could be capable of building atomic bombs. "You have to conclude this is not part of an energy program, this is part of a weapons program," John Pike, the founder of Globalsecurity.org , told Fox News.

Iran — one of three nations President Bush labeled as part of an "axis of evil" in 2003 — has come under heavy criticism by the international community for not doing away completely with its nuclear program, which has been under investigation for nearly two decades.

Iranian leaders argue that the nation is enriching the uranium in order to produce nuclear power; the United States says the program is a front for developing atomic weapons. Enrichment can be used to produce power or bombs.

The U.N. nuclear watchdog is investigating the photos. The U.S. intelligence community also has the images.

On Friday, the International Atomic Energy Agency (search ) censured Iran for past cover-ups in its nuclear program in a resolution that warned Tehran to be more forthcoming.

Iranian officials have said that if the United Nations were to pursue a resolution like that agreed upon Thursday, Tehran would continue with their enrichment program.

"I'm not at all sure that's a threat that should deter us that much," former Secretary of State Lawrence Eagleburger told Fox News. "I think we have a very serious problem and we'll have to pursue it very hard."

Before and After in Iran Images

The pictures of the Natanz facility — taken on Sept. 20, 2002 and Feb. 29, 2004 — show that Iran has been trying to cover up the compound, Pike said.

"We're really quite amazed at what we were seeing in this imagery and we're also quite amazed at what we're not seeing," Pike said.

Remarking on the most recent image, Pike said, "we don't see much of anything after all, it's basically just a big empty field, but if we had looked at it earlier, we can see this is their primary, their main enrichment facility."

The 2002 images show buildings under construction. But in the 2004 images, "you can see that they completely covered it up with a thick layer of dirt," Pike noted, perhaps to make it difficult to see it and harder for precision-guided munitions to target the underground facility.

A thick network of what could be fighting positions also encircle the plant, according to Pike's interpretation of the images.

"Possibly they would be fighting positions in case a commando raid was launched against this facility," Pike said. "It really looks like the Iranians have a fear someone is going to try to destroy this building before it can make bombs."

Alireza Jafarzadeh, a Fox News foreign affairs analyst, exposed the two sites on Aug. 14, 2002, after obtaining information from Iranian opposition forces with access to the regime.

Construction of buildings at Natanz began in 2000, he told Foxnews.com. There are two major parts, one of which consists of about six white buildings while three more in the images are under construction. In those three buildings are two large underground hallways.

It's in those hallways — one of which is about 32,000 square meters in size, the other is close to 8,000 square meters — Jafarzadeh said, where centrifuge machines are to be lined up.

"Once fully operational, it would have as many 50,000 centrifuge machines lined up there," he said. "These are the main enrichment halls that would produce enriched uranium en masse … once that's fully operational, perhaps just this site in Natanz would be able to produce 15 to 20 bombs a year."

The building is protected by 8-feet thick concrete walls, "primarily to protect it against air strikes," Jafarzadeh noted. Also, the entrance to the main building consists of a U-shaped tunnel.

"This way, even smart bombs cannot sort of glide or crawl into the hall," he said. "That tells me this is definitely built underground for air strike protection."

Photos of the Arak facility show that between Aug. 18, 2001 and Feb. 28, 2004, heavy construction took place at the plutonium-production facility.

"What is significant about this pictures — it shows how rapidly they have actually advanced in the construction of these sites," Jafarzadeh said.

"Because in such a short period of time, they have made big advancements … this facility can be used both for producing low-enrichment uranium, which as Iran claims, is for supporting fuel for nuclear reactors for what they call peaceful purposes and at the same time, it can be used for enriching uranium for weapons grade."

IAEA spokeswoman Melissa Fleming told Fox News that the agency first received allegations that these sites were used for nuclear bomb-making programs in 2002 and they immediately began "intensive" inspections that continue to this day.

"We are in Arak and Natanz quite frequently," she said.

Although the agency still has a number of questions about both sites, they "are both known to us and our investigation is focusing elsewhere right now," she said.

IAEA also has regular access to the scientists that work at both facilities and has visited the Natanz site since Feb. 29, 2004 and found nothing untoward, she said.

"If it had been razed we certainly would know something about it," she said of the site.

U.S.: Iran Denials 'Hollow'

Some experts warned that the satellite images can't be considered a smoking gun quite yet.

"It's clear Iran is trying to deal with the knowledge the IAEA has this two-decade long program," Daryl Kimball, executive director of the Arms Control Association (search), told Fox News on Friday. "I think it's unclear to me from this satellite imagery what's been hidden and what's not been hidden, which makes it all the more important for Iran to cooperate more fully" with weapons inspectors.

"We need to be careful that the pressure does not ratchet up so high that Iran kicks out inspectors" and closes the blinds to the global community about its nuclear activities, Kimball continued.

IAEA chief Mohamed ElBaradei (search) acknowledged Thursday that he had to revise one part of his report on Iran saying they had not disclosed the purchase of 15 magnets for P-2 centrifuges, when in fact Iran had admitted it in May.

Contrary to interpreting that as proof Iran is coming clean, State Department spokesman Richard Boucher said: "It only points out more how hollow Iran's denials and statements have been ... So we're once again left in the situation where we find that Iran has spent months and months and months denying things that were known, months and months trying to pretend that it was not doing things that finally became known and that it finally admitted."

Perhaps even more disconcerting, Boucher notes, is the satellite imagery showing Iran is actually trying to hide its activities.

"That report shows that Iran does have a track record of trying to hide clandestine nuclear activity since — for many years, including a practice of trying to remove equipment and sanitize buildings," Boucher said. "It's deplorable but not surprising that Iran's deception has gone to the extent of bulldozing entire sites to prevent the IAEA from discovering evidence of its nuclear weapons program."

Boucher said satellite images indicate that Iran has completely razed a different facility at Lavizan Shiyan, which the IAEA had not visited. The site first became known when an exiled Iranian opposition group said it was connected to a biological weapons program.

Jafarzadeh told Foxnews.com that at that site is now something called the Center for Readiness and New Defense Technology, which is affiliated to the defense ministry of the Iranian regime.

The center supposedly is part of new special military unit that now overseas all nuclear programs of the regime, separated from the "peaceful" uses of the program and under the control of the military, Jafarzadeh said. It's at this center where P-2 machines — more efficient enrichment devices used in producing the fuel used in nuclear power plants and atomic bombs — are allegedly produced.

A small number of fully assembled P-2 machines were found at one location in Iran earlier this year, U.S. and European officials said. Iran reportedly was looking to import 100,000 magnets, which can be used for 50,000 machines — two magnets for each machine.

"This raises serious concerns and fits a pattern, as I said, that we've seen from Iran of trying to cover up on its activities, including by trying to sanitize locations which the IAEA should be allowed to visit and expect," Boucher said.

Fox News' Amy Kellogg and Teri Schultz contributed to this report.