The offer is conditional, however, on world powers abandoning their push for a resolution against Iran at this week's meeting of the International Atomic Energy Agency's 35-member Board of Governors over its lack of co-operation with the IAEA, diplomats said, adding that the push was continuing.
During IAEA chief Rafael Grossi's trip to Iran last week, "the possibility of Iran not further expanding its stockpile of uranium enriched up to 60 per cent U-235 was discussed," read one of the two confidential quarterly IAEA reports, both seen by Reuters.
It added that the IAEA had verified that Iran had "begun implementation of preparatory measures".
Iran's offer was to cap the stock of uranium enriched to up to 60 per cent at around 185 kg, or the amount it had two days ago, a senior diplomat said.
That is enough in principle, if enriched further, for four nuclear weapons, according to an IAEA yardstick.
Iran denies seeking nuclear weapons.
The report said Iran's stock of uranium enriched to up to 60 per cent had grown by 17.6 kg since the previous report to 182.3 kg as of October 26, also enough for four weapons by that measure.
The second report said Iran had also agreed to consider allowing four more "experienced inspectors" to work in Iran after it barred most of the IAEA's inspectors who are experts in enrichment last year in what the IAEA called a "very serious blow" to its ability to do its job properly in Iran.
Although the senior diplomat said they could be enrichment experts, diplomats said they could not be the same experts that were barred.
The reports were delayed by Grossi's trip to Iran, during which he hoped to convince Iran's new President Masoud Pezeshkian to end a stand-off with the IAEA over long-standing issues like unexplained uranium traces at undeclared sites and extending IAEA oversight to more areas.
The draft resolution backed by the United Kingdom, France, Germany and the United States condemning Iran for its poor co-operation with the IAEA would also task the IAEA with issuing a "comprehensive report" on Iran's nuclear activities, diplomats said.
The aim is to pressure Iran to return to the negotiating table to agree fresh restrictions on its nuclear activities since a 2015 deal with far-ranging curbs fell apart.
Although most of its terms have been broken, the deal's "termination day" formally lifting them is in October of next year.
It is the last quarterly Board meeting before US president-elect Donald Trump takes office in January.
Trump pulled the United States out of the nuclear deal in 2018, which prompted its unravelling.
It is unclear if he would back talks with Iran.
