The International Atomic Energy Agency released a strongly worded report Tuesday saying its monitoring tasks in Iran had been "seriously undermined" after Tehran suspended some inspections of its nuclear activities.
The IAEA's latest report comes at a time when diplomatic efforts to revive a 2015 nuclear deal between Iran and world powers are at a standstill.
In February, Iran suspended some IAEA inspections in response to the United States' refusal to lift sanctions and also limited IAEA access to monitoring equipment such as cameras.
Initially, Iran reached a temporary agreement with the IAEA under which it committed to preserving recordings from this equipment with a view to eventually handing them over to the UN nuclear watchdog.
However, that agreement ran out on June 24 and Iran "has failed to engage with the Agency at all on this matter for a number of months", according to the report.
"Since 23 February 2021, the Agency's verification and monitoring activities have been seriously undermined as a result of Iran's decision to stop the implementation of its nuclear-related commitments", the report said.
A diplomatic source pointed out that the equipment was normally serviced every three months and that by now there would be a question over whether all the systems were "still operational".
According to the report, one of the cameras at a centrifuge component workshop at the city of Karaj was destroyed and another "severely damaged".
Iranian state television and Tasnim news agency reported in June that a "sabotage operation" had been thwarted at a building near Karaj belonging to the Atomic Energy Organisation of Iran.
- 'Not ready to talk' -
IAEA Director General Rafael Grossi has said he was available to go to Iran to meet the government of new ultra-conservative President Ebrahim Raisi.
However, no such visit has taken place, with one diplomatic source saying Iran was seemingly "not ready to talk" to the IAEA.
The IAEA said its confidence "that it can maintain continuity of knowledge is declining over time and has now significantly further declined" and the situation must be "immediately rectified by Iran".
The report added that Iran had boosted its stocks of uranium enriched above the levels allowed in the 2015 deal formally known as the Joint Comprehensive Plan of Action.
The JCPOA offered Iran an easing of Western and UN sanctions in return for tight controls on its nuclear programme, monitored by the UN.
Under the terms of the deal, Iran agreed not to enrich uranium above 3.67 percent, well below the 90-percent threshold needed for use in a nuclear weapon.
In addition, it was only allowed to have a stockpile of 202.8 kilograms in total -- equivalent to 300 kilograms in a particular compound form.
However, the Islamic republic has gradually rolled back its commitments since 2018 when then US president Donald Trump withdrew from the deal.
According to the latest report, Iran has now amassed a stockpile of 2,441.3 kilograms.
While it is less than in the IAEA's previous report in May, this is because some of the uranium enriched to a lower level has now been enriched to a higher level.
The total amount now includes 84.3 kilograms enriched to 20 percent, up from 62.8 kilograms in May, as well as 10 kilograms enriched up to 60 percent, up from 2.4 kilograms.
- 'Increasingly concerned' -
Several rounds of talks aiming at re-establishing the JCPOA took place in Vienna earlier this year but they broke up on June 20 with no date set to reconvene.
Iran warned last week that the talks might not be resumed for two to three months while Raisi's new government establishes itself.
Trump's successor President Joe Biden wants to bring Washington back into the 2015 nuclear deal.
Tehran is demanding all sanctions imposed or reimposed on it by the US since 2017 be lifted.
In a second report also issued on Tuesday the IAEA said there had been almost no progress on other outstanding queries over possible undeclared nuclear activity at several sites in Iran.
"The Director General is increasingly concerned that even after some two years the safeguards issues... remain unresolved," it said.
The US said that its special envoy for Iran, Robert Malley, "and a small delegation" will be travelling to Moscow and Paris this week "for consultations with our Russian and European partners on Iran's nuclear programme and the need to quickly reach and implement an understanding on a mutual return to compliance with the Joint Comprehensive Plan of Action."