An Iranian nuclear facility is so deep underground that U.S. airstrikes are unlikely to be able to reach it, according to experts and satellite images from the AP news agency.
Planet Labs PBC photos and videos show that Iran has been building tunnels in the mountain near the Natanz nuclear site, which has been the target of repeated sabotage attacks amid Tehran's standoff with the West over its nuclear program.
With Iran now producing uranium close to weapons-grade levels following the collapse of its nuclear deal with world powers, the facility complicates Western efforts to stop Tehran from potentially developing an atomic bomb, as diplomacy over its nuclear program remains stalled.
Completion of such a facility "would be a nightmare scenario that could trigger a new escalatory spiral," warned Kelsey Davenport, director of nonproliferation policy at the Washington-based Arms Control Association. "Given how close Iran is to having a bomb, it has very little room to escalate its program without crossing U.S. and Israeli red lines. So at this point, any further escalation increases the risk of conflict."
The construction at the Natanz site comes five years after then-President Donald Trump unilaterally withdrew the United States from the nuclear deal. Trump argued that the deal did not address Tehran's ballistic missile program, nor its support for militias in the Middle East.
But what it did do was strictly limit Iran's uranium enrichment to 3.67% purity, powerful enough only to power civilian power plants, and keep its stockpile at only about 300 kilograms (660 pounds).
Since the end of the nuclear deal, Iran has said it is enriching uranium to 60%, although inspectors recently found that the country had produced uranium particles at 83.7% purity. That is just one short step away from reaching the 90% threshold of weapons-grade uranium.
In February, international inspectors estimated that Iran's stockpile was more than 10 times what it was under the Obama-era deal, with enough enriched uranium to allow Tehran to make "several" nuclear bombs, according to the head of the International Atomic Energy Agency.
President Joe Biden and Israel's prime minister have said they will not allow Iran to build a nuclear weapon. "We believe diplomacy is the best way to achieve that goal, but the president has also made clear that we have not ruled out any options," the White House said in a statement to AP.
The Islamic Republic denies it is seeking nuclear weapons, although Tehran officials now talk openly about its ability to develop one.
Iran's mission to the United Nations said Iran's "peaceful nuclear activities are transparent and under International Atomic Energy Agency safeguards." However, Iran has limited access to international inspectors for years.
Iran says the new construction will replace an above-ground centrifuge manufacturing center in Natanz that was hit by an explosion and fire in July 2020. Tehran blamed the incident on Israel, which has long been suspected of conducting sabotage campaigns against its program.
Tehran has not acknowledged any other plans for the facility, although it would have to declare the site to the IAEA if it plans to introduce uranium there.
The new project is being built next to Natanz, about 225 kilometers (140 miles) south of Tehran. Natanz has been a source of international concern since its existence became known two decades ago.
Protected by anti-aircraft batteries, fences and Iran's paramilitary Revolutionary Guards, the facility spans 2.7 square kilometers (1 square mile) in the country's arid central highlands.
Satellite photos taken in April by Planet Labs PBC and analyzed by AP show that Iran is digging into K?h-e Kolang Gaz L? mountain, or "Picket Peak Mountain," which is just beyond the southern fence of Natanz.
A different set of images analyzed by the James Martin Center for Nonproliferation Studies reveals that four entrances have been dug into the side of the mountain, two to the east and two to the west. Each measures 6 meters (20 feet) wide and 8 meters (26 feet) high.
The extent of the work can be measured in large piles of earth, two to the west and one to the east. Based on the size of the rubble and other satellite data, experts at the center told AP that Iran is likely constructing a facility at a depth of between 80 meters (260 feet) and 100 meters (328 feet). The center's analysis, provided exclusively to AP, is the first to estimate the depth of the tunnel system based on satellite imagery.
The Institute for Science and International Security, a Washington-based nonprofit organization that has long been focused on Iran's nuclear program, suggested last year that the tunnels could be even deeper.
Experts say the size of the construction project indicates it is likely that Iran could use the subway facility to enrich uranium, not just to build centrifuges. Those tube-shaped centrifuges, arranged in large cascades of dozens of machines, rapidly spin uranium gas to enrich it. With additional cascades in operation, Iran could rapidly enrich uranium under the protection of the mountain.
"Therefore, the depth of the facility is of concern because it would be much more difficult to destroy with conventional weapons, such as a typical bunker-buster bomb," said Steven De La Fuente, a research associate at the center who led the analysis of the tunnel work.
The new Natanz facility is likely to be even deeper underground than Iran's Fordo facility, another enrichment site that was exposed in 2009 by U.S. and other leaders. That facility raised fears in the West that Iran was strengthening its airstrike program.
This subway facility led the U.S. to create the GBU-57 bomb, which can pass through at least 60 meters (200 feet) of earth before detonating, according to the U.S. military. U.S. officials have reportedly discussed the possibility of using two of these bombs in succession to be sure to destroy a site. It is unclear whether such an attack would damage a facility as deep as Natanz.
With these bombs potentially ruled out, the United States and its allies have fewer options for attacking the site. If diplomacy fails, sabotage attacks may resume.
Natanz has already been targeted by the Stuxnet virus, believed to have been created by Israel and the U.S., which destroyed Iranian centrifuges. Israel is also believed to have assassinated scientists involved in the program, targeted facilities with bomb-carrying drones and carried out other attacks. The Israeli government declined to comment.
Experts say such disruptive actions could bring Tehran even closer to the bomb and put its program even deeper into the mountain, where air strikes, sabotage and spies might not be able to reach it.
"Sabotage can reverse Iran's nuclear program in the short term, but it is not a viable long-term strategy to protect against a nuclear-armed Iran," said Davenport, the nonproliferation expert. "Making Iran's nuclear program even more subway increases the risk of proliferation."
(With information from AP)
International observers detected that Iran's regime is close to having enough uranium to manufacture a nuclear weapon
The UN warned that Iran has enough highly enriched uranium to build "several" nuclear weapons.