Iran on Sunday, July 5 confirmed that a damaged building at the underground Natanz nuclear site was a new centrifuge assembly center, the official IRNA news agency reported.

Iranian officials had previously sought to downplay the fire, which erupted early on Thursday, calling it only an “incident” that affected an “industrial shed.” However, a released photo and video of the site broadcast by Iranian state television showed a two-story brick building with scorch marks and its roof apparently destroyed.

A spokesman for Iran’s nuclear agency, Behrouz Kamalvandi, said Sunday that work had begun on the center in 2013 and it was inaugurated in 2018, TIME says.

“More advanced centrifuge machines were intended to be built there,” he said, adding that the damage would “possibly cause a delay in development and production of advanced centrifuge machines in the medium term.”

He said that the fire had damaged “precision and measuring instruments,” and that the center had not been operating at full capacity due to restrictions imposed by Tehran’s 2015 nuclear deal with world powers. Iran began experimenting with advanced centrifuge models in the wake of the U.S. unilaterally withdrawing from the deal two years ago.