FILE - In this photo released on Wednesday, Nov. 6, 2019 by the Atomic Energy Organization of Iran, a lift truck carries a cylinder…
FILE - In this photo released on Nov. 6, 2019 by the Atomic Energy Organization of Iran, a lift truck carries a cylinder containing uranium hexafluoride gas for the purpose of injecting the gas into centrifuges in Iran's Fordo nuclear facility.

DUBAI - Iran resumed uranium enrichment at its underground Fordow nuclear facility by injecting uranium gas into centrifuges, Iran's Tasnim news agency quoted the country's Atomic Energy Organization (AEOI) as saying on Thursday.

"After all successful preparations ... injection of uranium gas to centrifuges started on Thursday at Fordow ... all the process has been supervised by the inspectors of (the) U.N. nuclear watchdog," Tasnim reported, quoting the AEOI's statement.

A 2015 nuclear deal between Iran and major powers bans Fordow from producing nuclear material. But, with feedstock gas entering its centrifuges, the facility — built inside a mountain — will move from the permitted status of research plant to being an active nuclear site.

"The process will take a few hours to stabilize and by Saturday, when International Atomic Energy Agency inspectors will again visit the site, a uranium enrichment level of 4.5% will have been achieved," AEOI's spokesman Behrouz Kamalvandi told state TV.  Ninety percent purity is required for bomb-grade fuel.

In this photo released on Nov. 6, 2019, an Iran truck containing a cylinder of uranium hexafluoride gas leaves Ahmadi Roshan uranium enrichment facility in Natanz.

Iran has gradually scaled back its commitments to the deal, under which it curbed its nuclear program in exchange for the removal of most international sanctions, after the United States reneged on the agreement last year.

Under the pact, Iran agreed to turn Fordow into a "nuclear, physics and technology center" where 1,044 centrifuges are used for purposes other than enrichment, such as producing stable isotopes, which have a variety of civil uses.

"All the centrifuges installed in Fordow are IR1 types. Uranium  gas (UF6) was injected to four chains of IR1 centrifuges (696 centrifuges)," Kamalvandi said. "Two other remaining chains of IR1 centrifuges (348 centrifuges) will be used for producing and enriching stable isotopes in the facility."

U.S. President Donald Trump exited the deal, saying it was flawed to Iran's advantage. Washington has since renewed and intensified sanctions on Iran, slashing the country's economically vital crude oil sales by more than 80%. The measure will further complicate the chances of saving the accord, which European powers have called on Iran to respect.

Responding to Washington's "maximum pressure" policy, Iran has bypassed the restrictions of the deal step-by-step — including by breaching both its cap on stockpiled enriched uranium and on the fissile level of enrichment.