"Iran has informed the Agency that in order to comply with a legal act recently passed by the country's parliament, the Atomic Energy Organization of Iran intends to produce low-enriched uranium (LEU) up to 20 percent at the Fordow Fuel Enrichment Plant," officials with the International Atomic Energy Agency said in a statement, referring to an Iranian law passed after the recent assassination of a top nuclear scientist.
The Fordow plant -- which is built inside a mountain, apparently to protect it from aerial attack -- is not permitted to enrich uranium, according to the terms of the nuclear deal. However Iran had already restarted activity at the facility prior to Friday's announcement.
"Iran's letter to the Agency ... did not say when this enrichment activity would take place," the IAEA statement said. An IAEA official confirmed to ABC News that the Iranian letter was sent Thursday.
Most of the work in the enrichment process involves getting uranium to 20% -- so while Iran continues to insist its nuclear program is peaceful, such work would shorten the "breakout time" that it would take to develop a nuclear bomb.
The 2015 nuclear deal was designed to lengthen that time period, but the agreement is all but dead after the Trump administration pulled out, prompting Iran to stop abiding by many of the deal's requirements, including enrichment thresholds.
Friday's development could complicate things for the incoming Biden administration, which has said it wants to re-engage with Iran on its nuclear program. It also comes as tensions run high just days before the anniversary of the assassination of Iran's General Qassem Soleimani in a U.S. drone strike.