Iran plans to enrich uranium up to 20 per cent at its underground Fordo nuclear facility, international inspectors have said, pushing its program a technical step away from weapons-grade levels as it increases pressure on the West over its tattered atomic deal.
The International Atomic Energy Agency acknowledged on Saturday that Iran had informed its inspectors of the decision after news leaked overnight Friday.
The move comes amid heightened tensions between Iran and the US 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 US drone strike killing a top Iranian general in Baghdad a year ago, an anniversary coming on Sunday that has American officials now worried about possible retaliation by Iran.
The decision comes after 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 President-elect Joe Biden, who has said he's willing to re-enter the nuclear deal.
"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".
It also offered no time frame for starting the higher enrichment. Iran's mission to the United Nations did not immediately respond to a request for comment.
Since the deal's collapse, Iran has resumed enrichment at Fordo, near the holy Shiite city of Qom, some 90 kilometres southwest of Tehran.
The 2015 deal saw Iran agree to limit its enrichment in exchange for sanctions relief. The accord also called for Fordo to be turned into a research and development facility.
As of now, Iran is enriching uranium up to 4.5 per cent, in violation of the accord's limit of 3.67 per cent.
Experts say Iran now has enough low-enriched uranium stockpiled for at least two nuclear weapons, if it chose to pursue them. Iran long has maintained its nuclear program is peaceful.
Iran separately has begun construction on a new site at Fordo, according to satellite photos obtained by The Associated Press in December.
Iran's announcement coincides with the anniversary of the US drone striking Revolutionary Guard General Qassem Soleimani in Baghdad last year.
That attack later saw Iran retaliate by launching a ballistic missile strike injuring dozens of US troops in Iraq. Tehran also accidentally shot down a Ukrainian passenger jet that night, killing all 176 people on board.
As the anniversary approached, the US has sent B-52 bombers flying over the region and sent a nuclear-powered submarine into the Persian Gulf.
On Thursday, sailors discovered a limpet mine on a tanker in the Persian Gulf off Iraq near the Iranian border as it prepared to transfer fuel to another tanker owned by a company traded on the New York Stock Exchange.
No one has claimed responsibility for the mining, though it comes after a series of similar attacks in 2019 that the US Navy blamed on Iran. Tehran denied being involved.
In November, an Iranian scientist who founded the country's military nuclear program two decades earlier was killed in an attack Tehran blames on Israel.