Iran has not publicly confirmed any new construction at Fordo, whose revealing by the West in 2009 appeared in an earlier round of brinkmanship before world powers struck the 2015 nuclear deal with Tehran.
While the idea of the building remains unclear, any work at Fordo likely will trigger new concerns in the last days of the Trump administration before the inauguration of President-elect Joe Biden. Already, Iran is constructing its Natanz nuclear facility after a strange explosion in July there that Tehran reported as a sabotage attack.
“Any changes at this site will be carefully watched as a sign of where Iran’s nuclear program is headed,” said Jeffrey Lewis, a specialist at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies who studies Iran.
Iran’s embassy to the United Nations did not immediately respond to a request for comment. The International Atomic Energy Agency, whose investigators are in Iran as part of the nuclear deal, also did not immediately reply to a request for comment.
Construction on the Fordo site started in late September. Satellite images obtained from Maxar Technologies dispense the construction taking place at a northwest edge of the site, near the holy Shiite city of Qom, about 90 kilometers (55 miles) southwest of Tehran.
A Dec. 11 satellite photo reveals what seems to be a dug foundation for a building with dozens of pillars. Such pillars can be utilized in construction to support buildings in earthquake zones.
The construction site sits northwest of Fordo’s underground facility, formed deep inside a mountain to guard it against possible airstrikes. The site is near other support and research-and-development buildings at Fordo.
Among those buildings is Iran’s National Vacuum Technology Center. Vacuum technology is a critical component of Iran’s uranium-gas centrifuges, which enrich uranium.
A Twitter account called Observer IL earlier this week issued an image of Fordo revealing the construction, citing it as coming from South Korea’s Korea Aerospace Research Institute.
The AP later reached the Twitter user, who identified himself as a retired Israeli Defense Forces soldier with a civil engineering background. The Korea Aerospace Research Institute confirmed taking the satellite photo.
Trump in 2018 unilaterally withdrew the U.S. from Iran’s nuclear deal, in which Tehran had agreed to restrict its uranium enrichment in exchange for the lifting of economic sanctions. Since then Iran gradually and publicly broke the deal’s limits as a series of escalating incidents pushed the two countries to the brink of war at the beginning of the year. Tensions remain high.