A view of a damaged building after a fire broke out at Iran’s Natanz Nuclear Facility, in Isfahan, Iran, July 2, 2020. Photo: Atomic Energy Organization of Iran / WANA (West Asia News Agency) via Reuters.

Iran has begun to build a hall in “the heart of the mountains” near its Natanz nuclear site for making advanced centrifuges, Iran‘s nuclear chief said on Tuesday, aiming to replace a production hall at the facility hit by fire in July.

Iran said at the time that the fire was the result of sabotage and had caused significant damage that could slow the development of advanced uranium-enrichment centrifuges.

“Due to the sabotage, it was decided to build a more modern, larger and more comprehensive hall in all dimensions in the heart of the mountain near Natanz. Of course, the work has begun,” said Ali Akbar Salehi, according to state TV.

Natanz is the centerpiece of Iran‘s enrichment program. Western intelligence agencies and the UN’s nuclear watchdog (IAEA) believe Iran had a coordinated, clandestine nuclear arms program that it halted in 2003.

The Natanz uranium-enrichment site, much of which is underground, is one of several Iranian facilities monitored by inspectors of the IAEA.

A confrontation between arch foes Tehran and Washington has worsened since 2018, when US President Donald Trump withdrew from Iran’s 2015 nuclear deal with major powers and reimposed sanctions that have crippled Iran’s economy.

Under the deal, Iran agreed to curb its nuclear program in exchange for the removal of most international sanctions. In reaction to US sanctions, Tehran has gradually distanced itself from the nuclear pact.