DUBAI, United Arab Emirates (AP) — Iran 's president formally approved the resignation of one of his vice presidents who served as Tehran's key negotiator in its 2015 nuclear deal with world powers, just as the head of the United Nations' nuclear watchdog was due to arrive in the Islamic Republic on Wednesday.

President Masoud Pezeshkian's announcement late Tuesday regarding Mohammad Javad Zarif comes as Iran prepares for a second round of negotiations with the United States over its rapidly advancing nuclear program.

Meanwhile, the visit by Rafael Mariano Grossi, the head of the International Atomic Energy Agency, scheduled to start Wednesday may include negotiations over just what access his inspectors can get under any proposed deal.

The stakes of the negotiations couldn’t be higher for the two nations closing in on half a century of enmity. U.S. President Donald Trump repeatedly has threatened to unleash airstrikes targeting Iran’s nuclear program if a deal isn’t reached. Iranian officials increasingly warn that they could pursue a nuclear weapon with their stockpile of uranium enriched to near weapons-grade levels.

Zarif served as a key supporter of Pezeshkian in his election last year but drew criticism from hard-liners within Iran's Shiite theocracy, who long have alleged Zarif gave away too much in negotiations.

In March, Zarif tendered his resignation to Pezeshkian. However, the president did not immediately respond to the letter. Zarif has used resignation announcements in the past in his political career as leverage, including in a dispute last year over the composition of Pezeshkian’s Cabinet. The president had rejected that resignation.

But on late Tuesday, a statement from the presidency said Pezeshkian wrote Zarif a letter praising him but accepting his resignation.

“Pezeshkian emphasized that due to certain issues, his administration can no longer benefit from Zarif’s valuable knowledge and expertise,” a statement from the presidency said.

The president in a decree appointed Mohsen Ismaili, 59, to be his new vice president for strategic affairs. In Iran's political system, the president has multiple vice presidents. Ismaili is known as a political moderate and a legal expert.

Grossi meanwhile was due to arrive in Tehran and have meetings with Pezeshkian and others.

Since the nuclear deal’s collapse in 2018 with Trump's unilateral withdraw of the U.S. from the accord, Iran has abandoned all limits on its program, and enriches uranium to up to 60% purity — near weapons-grade levels of 90%.

Surveillance cameras installed by the IAEA have been disrupted, while Iran has barred some of the Vienna-based agency’s most experienced inspectors. Iranian officials also have increasingly threatened that they could pursue atomic weapons, something the West and the IAEA have been worried about for years since Tehran abandoned an organized weapons program in 2003.

Any possible deal between Iran and the U.S. likely would need to rely on the IAEA's expertise to ensure Tehran's compliance. And despite tensions between Iran and the agency, its access has not been entirely revoked.

It remains unclear where the next round of talks will be held, though they are scheduled for Saturday. Officials initially identified Rome as hosting the negotiations, only for Iran to insist early Tuesday they would return to Oman. American officials so far haven’t said where the talks will be held, though Trump did call Oman’s Sultan Haitham bin Tariq on Tuesday while the ruler was on a trip to the Netherlands.

Meanwhile, Iran's Foreign Minister Abbas Araghchi on Wednesday warned the U.S. about taking contradictory stances in the talks.

That likely refers to comments from U.S. Mideast envoy Steve Witkoff, who this week initially suggested a deal could see Iran go back to 3.67% uranium enrichment — like in the 2015 deal reached by the Obama administration. Witkoff then followed up with saying "a deal with Iran will only be completed if it is a Trump deal.”

“Iran must stop and eliminate its nuclear enrichment and weaponization program,” he wrote on the social platform X. “It is imperative for the world that we create a tough, fair deal that will endure, and that is what President Trump has asked me to do.”

Araghchi warned America about taking any “contradictory and opposing stances” in the talks.

“Enrichment is a real and accepted issue, and we are ready for trust building about possible concerns," Araghchi said. But losing the right to enrich at all "is not negotiable.”

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Karimi reported from Tehran, Iran.