The decision serves as pressure ahead of the inauguration of President-elect Joe Biden, who has said he is willing to re-enter the Iran nuclear deal.
Any work at the Fordo facility likely will trigger new concern in the waning days of the Trump administration.
Iran's defense minister vowed to continue Mohsen Fakhrizadeh’s work “with more speed and more power.”
Iran’s Supreme Leader Ayatollah Ali Khamenei said there would be a "definitive punishment of the perpetrators and those who ordered it."
Jahane Sanat had published an interview with an epidemiologist who said Iran's official COVID-19 figures account for only 5% of the real toll.
Iranian officials had downplayed the fire, which could set back the country's development of advanced centrifuge models.
The Natanz nuclear site is one of the most-tightly guarded sites in all of Iran.
Tehran accuses Trump and 35 others of involvement in the January drone strike that killed Gen. Qassem Soleimani in Baghdad.
The country has reportedly unveiled what experts described as a secret space program with a surprise launch.
Nearly 300 people have been killed and more than 1,000 sickened by ingesting methanol in the mistaken belief it protects against the new coronavirus.