Iran said cameras at the site were damaged during what it called an Israeli "sabotage" operation.
Iran has informed the International Atomic Energy Agency it has stopped production at one of its nuclear facilities attacked last June and transferred work to another site, the watchdog said Monday.
The move responded to a "security concern" following the attack, with the new site "better protected", a European diplomat told AFP.
The TESA complex in Karaj, which is near the capital Tehran, hosted a workshop to build components for centrifuges, machines used to enrich uranium.
Iran said cameras at the site were damaged on June 23, 2021 during what it called an Israeli "sabotage" operation.
In the aftermath, the Vienna-based IAEA said it did not receive permission to gain access and replace the surveillance equipment damaged in the attack.
The two parties finally struck an agreement in December and new cameras were installed.
However, IAEA Director General Rafael Mariano Grossi said "Iran had informed the Agency on 19 January that it intended to produce centrifuge rotor tubes and bellows at a new location in Esfahan," according to the UN watchdog.
It said "the Agency could adjust its surveillance and monitoring measures accordingly".
"A few days later, Agency inspectors applied seals on all the relevant machines in the Karaj workshop, placed them under containment and then removed the surveillance cameras installed there," it said.
"As a result, the production of centrifuge rotor tubes and bellows at the Karaj workshop had ceased," it added.
Then on January 24 IAEA inspectors set up cameras at a site in Esfahan "to ensure the machines intended for the production of centrifuge rotor tubes and bellows were under monitoring", it said.
It added that the production of the centrifuge equipment at the new workshop had yet to begin.
Iran has sharply accelerated its nuclear activities in the years since US president Donald Trump withdrew from the 2015 international nuclear deal and imposed sweeping sanctions on Tehran.
The 2015 deal -- struck between Iran and the United States (under president Barack Obama), Germany, France, Britain, China and Russia -- offered Iran drastic relief from international sanctions in return for draconian curbs on its nuclear programme.
After President Joe Biden entered the White House just over a year ago, talks to revive the nuclear deal began in April 2021 in Vienna.
But they stopped for several months as the Islamic republic elected a new ultraconservative government.
The talks finally resumed in late November and are now in their final phase that requires political decisions, according to parties involved in the talks.