DUBAI, United Arab Emirates (AP) — Iran has told international nuclear inspectors it plans to enrich uranium up to 20% at its underground Fordo nuclear facility, a technical step away from weapons-grade levels, as it increases pressure on the West over its tattered atomic deal.

Iran’s state-run IRNA news agency acknowledged the step after news of a letter it sent to the International Atomic Energy Agency leaked overnight Friday. Russia’s representative to the IAEA similarly acknowledged Iran’s letter on Twitter, though the agency did not immediately respond to a request for comment early Saturday.

The move comes amid heightened tensions between Iran and the U.S. in the waning days of the administration of President Donald Trump, who unilaterally withdrew America from Tehran’s nuclear deal in 2018. That set in motion an escalating series of incidents capped by a U.S. drone strike killing a top Iranian general in Baghdad a year ago, an anniversary coming Sunday that has American officials now worried about possible retaliation by Iran.

The decision comes after parliament passed a bill, later approved by a constitutional watchdog, aimed at hiking enrichment to pressure Europe into providing sanctions relief.

Mikhail Ulyanov, Russia’s permanent representative to the Vienna-based IAEA, wrote on Twitter that Tehran planned to resume enrichment up to 20% after the Wall Street Journal broke the news.

IRNA later reported Ulyanov’s comments, linking the decision to the parliament bill aimed at restarting higher enrichment at Iran’s underground Fordo facility.

Since the deal’s collapse, Iran has resumed enrichment at Fordo, near the holy Shiite city of Qom, some 55 miles southwest of Tehran.

Shielded by the mountains, Fordo is ringed by anti-aircraft guns and other fortifications. It is about the size of a football field, large enough to house 3,000 centrifuges, but small and hardened enough to lead U.S. officials to suspect it had a military purpose when they exposed the site publicly in 2009.

As of now, Iran is enriching uranium up to 4.5%, in violation of the accord’s limit of 3.67%. Experts say Iran now has enough low-enriched uranium stockpiled for at least two nuclear weapons, if it chose to pursue them. Iran long has maintained its nuclear program is peaceful.

Iran separately has begun construction on a new site at its underground nuclear facility at Fordo, according to satellite photos obtained by The Associated Press in December.

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