Iran has made 55 kg of uranium enriched to up to 20 percent - the point at which it is highly enriched - indicating quicker production than the 10 kg a month rate required by an Iranian law that created the process in January, Iranian authorities said on Wednesday.
The disclosure comes a day after Tehran and Washington held what they described as "constructive" indirect talks in Vienna on Tuesday aimed at finding ways to revive a 2015 nuclear deal between Iran and world powers.
Iran's hardline parliament passed a law last year that obliges the government to harden its nuclear stance, partly in reaction to former President Donald Trump's withdrawal from the nuclear deal in 2018.
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Trump's withdrawal prompted Iran to steadily overstep the accord's limits on its nuclear program designed to make it harder to develop an atomic bomb - an ambition Tehran denies.
The law required Iran to start enriching to 20 percent and stipulated that at least 120 kg (265 pounds) of uranium refined to that level be made each year, which amounts to 10 kg a month.
Iran's production rate is already "up to 40 percent" faster than that, Atomic Energy Organization spokesman Behrouz Kamalvandi indicated.
"In less than four months we have produced 55 kg of 20 percent enriched uranium ... in around eight months we can reach 120 kg," Kamalvandi told state TV.
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Uranium is considered highly enriched as of 20 percent. Enriching to 20 percent is a big step towards enriching to weapons-grade.
A quarterly report on Iran's nuclear activities by the UN nuclear watchdog in February said that as of February 16, Iran had produced 17.6 kg of uranium enriched up to 20 percent, with the next level down being enriched between 2-5 percent.
A senior diplomat said at the time that Iran was producing uranium enriched to 20 percent at a rate of 15 kg per month.
As part of a recent acceleration of its breaches of the nuclear deal, in January Iran began enriching uranium to 20 percent at Fordow, an underground uranium enrichment site that was built in secret inside a mountain possibly to withstand any aerial bombardment.
Under the deal, Tehran is not allowed to enrich uranium at Fordow at all.
Until January, Iran had not enriched beyond 4.5 percent purity - above the deal's limit of 3.67 percent but still far below the 20 percent it achieved before the deal, or the 90 percent that is weapons-grade.