Iran has informed the director general of the International Atomic Energy Agency (IAEA) that it will begin 60% uranium enrichment, Deputy Foreign Minister Abbas Araghchi told reporters as he arrived to Vienna on Tuesday for a second round of nuclear talks.

Why it matters: This will be Iran's most severe violation of the 2015 nuclear deal since the Trump administration withdrew from the agreement in 2018. It's also a serious blow to the ongoing efforts to salvage the deal.

• The announcement comes in response to the explosion at the Natanz uranium enrichment facility, for which Iran blames Israel.
• It will leave Iran short of the 90% enrichment necessary to produce a nuclear weapon, but bring Iran closer to that threshold than ever before.
• Iran had been enriching to 20% since January. That's also the level at which Tehran was enriching prior to the nuclear deal.
• Araghchi added that another 1,000 centrifuges with 50% more enrichment capacity will be added in Natanz, in addition to replacing the damaged centrifuges.

The state of play: The resumption of the Vienna talks has been postponed from Wednesday to Thursday because a member of the EU delegation tested positive for COVID-19, Araghchi said.

• Meanwhile, senior officials from the U.S. and Israel will meet Tuesday for a strategic dialogue on Iran.
• The Biden administration has distanced itself from the Natanz explosion and said it hopes the Vienna talks will proceed as planned.
• The latest: Shortly after the Iranian announcement, Lebanese and Iranian media outlets reported that an Israeli-owned ship was attacked in the Gulf of Oman. Israeli officials confirmed the reports and said Iran is likely behind the attack.

Update: White House Press Secretary Jen Psaki said the "provocative Iranian announcement... calls into question Iran's seriousness" in the negotiations, but also stressed the U.S. would continue diplomacy with Iran.

What's next: The U.S. and Israel are expected to hold a third round of strategic talks on Iran at the end of April.

• The White House said that during the round of virtual talks held today between the parties National Security Adviser Jake Sullivan "warmly invited" his Israeli counterpart, Meir Ben-Shabbat, to visit Washington before the end of this month for follow-up consultations.

Go deeper: "Nuclear sabotage" in Iran threatens nuclear talks in Vienna