“Thanks to our diligent nuclear scientists, two cascades of 348 IR-2m centrifuges with almost four times the capacity of IR1 are now running with UF6 successfully in Natanz,” Kazem Gharibabadi said in a tweet.

He promised there is “more to come soon,” and announced that the installation of two cascades of IR6 centrifuges was also underway in Fordow, another of Iran’s nuclear sites.

The envoy to the UN’s nuclear watchdog in Vienna added that the agency had been “informed of the progress as planned.”

The IAEA is yet to comment publicly on the matter, but Reuters said on Tuesday it had obtained a confidential report from the agency showing that Iran has started enriching uranium with 174 IR-2m centrifuges underground at Natanz.

The country was already enriching uranium with a set of the advanced machinery at the plant last year, but the IAEA has reportedly said that a third cascade is nearly ready for use and a fourth is being installed.

Last week, the spokesman for the Atomic Energy Organization of Iran (AEOI), Behrouz Kamalvandi, said 1,000 of the IR-2m centrifuges would be installed within three months.

Iran’s enrichment of uranium is strictly limited by the Joint Comprehensive Plan of Action (JCPOA) signed with major world powers in 2015.