The Azadi Tower is illuminated in Tehran, Iran, on Jan 1, 2021, during a ceremony on the occasion of first anniversary of death of Qassem Soleimani, former commander of the Quds Force of Iran's Islamic Revolution Guards Corps (IRGC). (Photo by Ahmad Halabisaz/Xinhua)

Iran confirmed Tuesday it is now enriching uranium to 20 percent purity, well beyond the threshold set by its 2015 nuclear deal with major powers. 

The move at its underground Fordow facility was confirmed by UN watchdog the International Atomic Energy Agency (IAEA).

It was the most striking suspension yet of Iranian commitments under the landmark deal, a process it started in 2019 in response to US President Donald Trump's dramatic withdrawal from the accord the previous year.

"At around 7 pm (1530 GMT Monday), we reached 20 percent" enrichment, spokesperson Behrouz Kamalavandi told state TV in an interview aired on Tuesday.

Announcing the move on Monday, government spokesperson Ali Rabiei said President Hassan Rouhani had ordered the enrichment "in recent days" in line with a law passed last month by the parliament.

The law "for the lifting of sanctions and protection of the Iranian people's interests" mandates Rouhani's government to "produce and store 120 kilograms per year of uranium enriched to 20 percent."

Iran's Foreign Minister Javad Zarif tweeted that "we resumed 20 percent enrichment as legislated by our parliament," adding that the IAEA had been "duly notified." He stressed that Tehran took the step "after years of non-compliance" by other parties and that "our measures are fully reversible upon full compliance by all."

The step comes less than three weeks before the end of the presidency of Trump, who has sought to economically punish and diplomatically isolate Iran with a "maximum pressure" campaign, including tough sanctions.

The Iranian government has signaled a readiness to engage with US President-elect Joe Biden, who has expressed willingness to return to diplomacy with Tehran and takes office on January 20.

Iran's return to enrichment of uranium to 20 percent purity has triggered international concern because it is seen as a significant step toward the 90 percent level required for a nuclear weapon.

The IAEA confirmed that "Iran today began feeding uranium already enriched up to 4.1 percent U-235 into six centrifuge cascades at the Fordow Fuel Enrichment Plant for further enrichment up to 20 percent."