The step was seen as a significant step taken by Iran's nuclear programme in response to the UN nuclear watchdog resolution calling for Tehran to cooperate in its probe.
Iran has announced its decision to ramp up the production of uranium at an underground nuclear facility in response to the recent resolution passed by the UN nuclear watchdog.
The Atomic Energy Organisation of Iran, as cited by state media, said it began to produce uranium up to 60 percent purity at the Fordow facility, located 32 kilometres northeast of the Iranian city of Qom.
The step was seen as a significant addition to the country's nuclear programme.
Iran’s nuclear agency said it has informed the International Atomic Energy Agency (IAEA), the UN nuclear agency, of the decision in a letter, calling it a "strong response" to the agency's recent resolution.
Enrichment to 60 percent purity is one short, technical step away from weapons-grade level of 90 percent.
Nonproliferation experts have warned in recent months that Iran now has enough 60 percent-enriched uranium to reprocess into fuel for at least one nuclear bomb.
Iran is already enriching to 60 percent purity at its Natanz nuclear facility in central Iran.
In the last two years, Iran has significantly ramped up its uranium enrichment activities from 3.67 percent stipulated under the 2015 nuclear deal to 60 percent, sparking concerns in the West.
Iranian authorities say the measures are reversible if the US returns to the deal it abandoned in May 2018 and lifts sanctions imposed by the previous US administration.
Two new centrifuge cascades
Iran also announced that two new centrifuge cascades, IR-2m and IR-4, were reviewed and operated at the Natanz nuclear facility in the central Isfahan province, while two others will be fed in the coming days.
There are also plans to replace the IR-1 centrifuges at Fordow with advanced IR-6 centrifuges. The process of equipping a hall at the facility with eight new chains will be executed in several stages.
The UN watchdog's 35-member board of governors passed a resolution last week, asking Iran to urgently cooperate with its investigation into uranium traces found at three undeclared sites.
In its statement to the board after the resolution was adopted with 26 votes in favour and two abstentions, the US said Iran “must now provide the necessary cooperation, no more empty promises.”
Following the latest IAEA resolution, top Iranian officials warned of “retaliatory measures.”
Iran’s envoy to the IAEA, Mohsen Naziri, dismissed the resolution and said it could “impact the constructive relations between Tehran and the agency,” accusing the agency of “political goals.”
It is the second resolution passed by the IAEA this year calling on Iran to cooperate with its probe.