The decision to add the two IR-6 centrifuges cascades at its underground Natanz nuclear facility comes as countries at an International Atomic Energy Agency (IAEA) meeting in Vienna voted on Wednesday night to censure Iran.
The rebuke deals with what the watchdog refers to as Iran’s failure to provide “credible information” over man-made nuclear material found at three undeclared sites in the country.
But even before the vote, Iran shut off two devices the IAEA uses to monitor enrichment at Natanz.
Iranian officials also threatened to take more steps amid a years-long crisis that threatens to widen into further attacks.
The IAEA said on Thursday that its director-general Rafael Mariano Grossi told members that Iran informed the agency that it planned to install two new cascades of the IR-6 at Natanz.
A cascade is a series of centrifuges hooked together to rapidly spin uranium gas to enrich it.
An IR-6 centrifuge spins uranium 10 times as fast as the first-generation centrifuges that Iran was once limited to under its 2015 nuclear deal with world powers.
As of February, Iran had already been spinning a cascade of IR-6s at its underground facility at Fordo, according to the IAEA.
At Natanz, located some 200 kilometres (125 miles) south of the capital Tehran, Iran earlier said it planned to install one cascade of IR-6s.
The IAEA said it “verified” the ongoing installation of that cascade on Monday, while the newly promised two new cascades had yet to begin.
Iran and world powers agreed in 2015 to the nuclear deal, which saw Tehran drastically limit its enrichment of uranium in exchange for the lifting of economic sanctions.
In 2018, then-US president Donald Trump unilaterally withdrew America from the accord, raising tensions across the wider Middle East and sparking a series of attacks and incidents.
Talks in Vienna over Iran’s tattered nuclear deal have been stalled since April.
Since the deal’s collapse, Iran runs advanced centrifuges and has a rapidly growing stockpile of enriched uranium.
Non-proliferation experts warn Iran has enriched enough up to 60% purity – a short technical step from weapons-grade levels of 90% – to make one nuclear weapon should it decide to do so.
Iran insists its programme is for peaceful purposes, though UN experts and western intelligence agencies say Iran had an organised military nuclear programme through 2003.
Building a nuclear bomb would still take Iran more time if it pursued a weapon, analysts say, though they warn Tehran’s advances make the programme more dangerous.
Israel has threatened in the past that it would carry out a pre-emptive strike to stop Iran – and is already suspected in a series of recent killings targeting Iranian officials.
Iran has already been holding footage from IAEA surveillance cameras since February 2021 as a pressure tactic to restore the atomic accord.
The censure resolution at the IAEA meeting in Vienna, sponsored by Germany, France, the UK and US, passed with the support of 30 of 35 governors.
Russia and China voted against, Russian ambassador Mikhail Ulyanov wrote on Twitter.
India, Libya and Pakistan abstained.
After the vote, a joint statement from France, Germany, the UK and the US said the censure “sends an unambiguous message to Iran that it must meet its safeguards obligations and provide technically credible clarifications on outstanding safeguards issues”.
Iran’s Foreign Ministry meanwhile criticised the censure as a “political, incorrect and unconstructive action”.
An Iranian official earlier warned IAEA officials that Tehran was now considering taking “other measures” as well.
“We hope that they come to their senses and respond to Iran’s co-operation with co-operation,” said Behrouz Kamalvandi, a spokesman for the Atomic Energy Organisation of Iran.
“It is not acceptable that they show inappropriate behaviour while Iran continues to co-operate.”
On Wednesday night, a drone exploded in the northern Iraqi city of Irbil in its Kurdish region, slightly wounding three people and damaging cars and a nearby restaurant, officials said.
While no-one immediately claimed the attack, Iran has targeted Irbil in the past amid the regional tensions.