Iran on Monday resumed 20 percent uranium enrichment at its sensitive Fordow nuclear facility, state media reported — a major step away from a 2015 nuclear deal struck with world powers. The move could complicate the incoming Biden administration’s plans to restart nuclear talks with Tehran. Iranian forces also seized a South Korean-flagged ship transiting the Persian Gulf.

The enrichment process at Fordow — an underground facility near the holy city of Qom — began earlier Monday, government spokesman Ali Rabie said. He said Iran had notified the International Atomic Energy Agency, the United Nations’ nuclear watchdog.

A spokesman for the agency said Monday that its inspectors were monitoring activities at Fordow and that IAEA Director General Rafael Mariano Grossi was expected to submit a report to the watchdog’s member states later in the day, Reuters reported.

Under the 2015 nuclear agreement, which restricted the size and purity of Iran’s enriched-uranium stockpile, Tehran is banned from enriching uranium at the Fordow site or even bringing uranium there for 15 years from the start of the accord. The site was revealed as a covert enrichment facility by Britain, France and the United States in 2009.