The move comes amid heightened tensions between Iran and the U.S. in the waning days of the administration of President Donald Trump, who unilaterally withdrew America from Tehran's nuclear deal in 2018.
That set in motion an escalating series of incidents capped by a U.S. drone strike that killed a top Iranian general in Baghdad a year ago, an anniversary coming Sunday that has American officials now worried about possible retaliation by Iran.
Iran's decision to begin enriching to 20% a decade ago nearly brought an Israeli strike targeting its nuclear facilities, tensions that only abated with the 2015 atomic deal. A resumption of 20% enrichment could see that brinksmanship return.
Even Ali Akbar Salehi, the U.S.-educated head of the civilian Atomic Energy Organization of Iran, offered a military analogy to describe his agency's readiness to take the next step.
"We are like soldiers and our fingers are on the triggers," Salehi told Iranian state television. "The commander should command and we shoot. We are ready for this and will produce (20% enriched uranium) as soon as possible."
Iran's decision comes after its parliament passed a bill, later approved by a constitutional watchdog, aimed at hiking enrichment to pressure Europe into providing sanctions relief. It also serves as pressure ahead of the inauguration of U.S. President-elect Joe Biden, who has said he is willing to re-enter the nuclear deal.
The International Atomic Energy Agency acknowledged Iran had informed its inspectors of the decision by a letter after news leaked overnight Friday.
"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 ... up to 20 percent at the Fordo Fuel Enrichment Plant," the IAEA said in a statement.
The IAEA added Iran did not say when it planned to boost enrichment, though the agency "has inspectors present in Iran on a 24/7 basis and they have regular access to Fordo." The parliamentary bill also called on Iran to expel those inspectors, though it appears Tehran still hasn't decided to take that step.
Salehi said Iran would need to switch out natural uranium in centrifuges at Fordo for material already enriched to 4% to begin the process of going to 20%.
"It should be done under IAEA supervision," Salehi added.