Iran, however, has slowed down the pace at which it produces uranium enriched up to 60 percent -- close to bomb-grade -- according to the International Atomic Energy Agency (IAEA).

Its overall stockpile of enriched uranium also decreased -- due to technical reasons -- and it's still far beyond the limit set in a now-tattered 2015 accord between Tehran and world powers.

The two confidential reports seen by AFP come days before the IAEA board of governors is due to meet to review Iran's progress in addressing the watchdog's concerns.

The agency noted that "no further progress" has been made in reinstalling some monitoring equipment set up under the 2015 nuclear deal -- but which was later removed by Iran.

Tehran in March vowed to reactivate surveillance devices, which it disconnected in June 2022 amid deteriorating relations with the West.

The IAEA also deplored that it has had no access to any of the data recorded by its surveillance cameras since February 2021.

"Since June 2022, the only recorded data that exists is that collected by cameras installed at workshops in Esfahan in May 2023," it said, adding that it is "indispensable" that Iran provides access to "all existing recorded data".

Referring to Iran's lack of progress in explaining undeclared nuclear material found at Turquzabad and Varamin, the IAEA said it "requests Iran to work with the agency in earnest and in a sustained way towards the fulfilment of the commitments".

The thorny issue has long exacerbated relations between the two parties.

- Slower production rate -

In a separate report, the IAEA said Iran's total stockpile of enriched uranium was lower than in May, but still more than 18 times the limit set in the 2015 accord.

Iran's total enriched uranium stockpile was estimated at 3,795.5 kilogrammes (8,367.7 pounds) as of August 19, down by 949 kilogrammes from May, the agency said.

The limit in the 2015 deal was set at 202.8 kilogrammes.

The stockpile of uranium that is enriched to up to 60 percent is now at 121.6 kilos, up from 114.1 kilos in May.

Enrichment levels of around 90 percent are required for use in a nuclear weapon.

The slowdown in growth of Iran's stockpile of near bomb-grade uranium might be due to a political or technical decision, a senior diplomat said.

The production rate has slowed to about one third of what it used to be in previous months, the diplomat added.

Iran also has 535.8 kilos of uranium enriched up to 20 percent, up from 470.9 kilos in the last May report.

The landmark 2015 deal -- curbing Iran's nuclear programme in exchange for sanctions relief -- started to fall apart in 2018 when the US unilaterally withdrew from it and reimposed sanctions.

Efforts to revive it -- bringing Washington back into the deal and scaling back Tehran's programme again -- have been fruitless so far with European-led talks on hold since 2022.

Tensions between Tehran and Washington eased last month with the announcement of an agreement for Iran to release five American prisoners in exchange for the return of $6 billion in Iranian funds frozen in South Korea.

But the delicate agreement does not include the possibility of a return to the nuclear deal in the run-up to the 2024 US presidential election.