Tehran, Iran — An "incident" damaged an under-construction building Thursday near's underground Natanz nuclear enrichment facility, though it did not affect its centrifuge operations or cause any release of radiation, a spokesman said. The affected building, described as an "industrial shed," was above ground and not part of the enrichment facility itself, said Behrouz Kamalvandi, a spokesman for the Atomic Energy Organization of Iran.
Outside experts, however, said a building seriously damaged in the fire appeared to be a newly constructed centrifuge construction facility. The state-run IRNA news agency quoted Kamalvandi as saying there was "no need for concern" over the incident.
"There are physical and financial damages and we are investigating to assess," Kamalvandi later told Iranian state television. "Furthermore, there has been no interruption in the work of the enrichment site. Thank God, the site is continuing its work as before."
However, there was no previously announced construction work at Natanz, a uranium enrichment center some 155 miles south of the capital, Tehran. Natanz includes underground facilities buried under some 25 feet of concrete, which offers protection from airstrikes. The incident also appeared serious enough for both Kamalvandi and Iranian nuclear chief Ali Akbar Salehi to rush to Natanz.
Ramazanali Ferdowsi, the governor of the town of Natanz, later described the incident as a "fire." Ferdowsi said both firefighters and rescue teams deployed to the site to handle the incident. He offered no cause for the blaze in his remarks reported by the semiofficial Tasnim news agency.
Natanz, also known as the Pilot Fuel Enrichment Plant, is among the sites now monitored by the International Atomic Energy Agency after Iran's 2015 nuclear deal with world powers. The IAEA did not immediately respond to a request for comment over the incident.
Data collected by a U.S. National Oceanic and Atmospheric Administration satellite suggested the fire broke out around 2 a.m. local time in the northwest corner of the Natanz compound. Flames from the blaze were bright enough to be detected by the satellite from space.
The site of the fire corresponds to a newly opened centrifuge production facility, said Fabian Hinz, a researcher at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies in Monterey, California. He said he relied on satellite images and a state TV program on the facility to locate the building, which sits in Natanz's northwest corner.
David Albright of the Institute for Science and International Security similarly said the fire struck the production facility. His institute previously wrote a report on the new plant, identifying it from satellite pictures while it was under construction and later built.
Iranian nuclear officials did not respond to a request for comment about the analysts' comments.
Located in Iran's central Isfahan province, Natanz hosts the country's main uranium enrichment facility. There, centrifuges rapidly spin uranium hexafluoride gas to enrich uranium. Currently, the IAEA says Iran enriches uranium to about 4.5% purity, above the terms of the nuclear deal, but far below weapons-grade levels of 90%. It also has conducted tests on advanced centrifuges, according to the IAEA.
The U.S. under President Donald Trump unilaterally withdrew from the nuclear deal in May 2018, setting up months of. Iran now is breaking all the production limits set by the deal, but still allows IAEA inspectors and cameras to watch its nuclear sites.
However, Natanz did become a point of controversy last year as Iranian officials refused to allow an IAEA inspector into the facility in October after tests allegedly showed suspected traces of explosive nitrates. Nitrates are a common fertilizer. However, when mixed with proper amounts of fuel, the material can become an explosive as powerful as TNT. Swab tests, common at airports and other secure facilities, can detect its presence on the skin or objects.
Natanz also remains of particular concern to Tehran as it has been targeted for sabotage before. The Stuxnet computer virus, widely believed to be an American and Israeli creation, disrupted and destroyed centrifuges at Natanz amid the height of Western concerns over Iran's nuclear program.
Satellite photos show an explosion last Friday that rattled Iran's capital came from an area in its eastern mountains that analysts believe hides an underground tunnel system and missile production sites.
Iran has blamed the blast on a gas leak in what it describes a "public area."
Last Tuesday Iranian officials said another explosion, this one at at medical clinic in northern Tehran, left 19 people dead. That blast was also blamed on a gas leak.