International Atomic Energy Agency Director-General Rafael Grossi arrived in Tehran on Wednesday at the head of a fourteen-member inspection team, the agency’s first visit to Iran since the April 15 ceasefire and its first attempt to enter the nuclear facilities struck by Israeli aircraft during six weeks of war.

Grossi’s Airbus from Vienna landed at Imam Khomeini International Airport shortly before 9 a.m. local time and was met on the tarmac by Mohammad Eslami, the head of the Atomic Energy Organization of Iran, and by a deputy foreign minister. The director-general declined to take questions at the airport, telling reporters only that the visit was “technical, not political,” and that the agency intended to “look, measure and report.”

The mission is the centerpiece of the verification pillar of the phase-two ceasefire architecture that mediators in Islamabad spent the past week assembling. Under a protocol confirmed by Iranian Foreign Minister Abbas Araghchi at the Doha prisoner exchange on Saturday and reaffirmed in a letter from Eslami to the agency on Monday, IAEA inspectors will be granted access over the next ten days to three sites that featured prominently in Israeli targeting during the war: the underground enrichment hall at Fordow, the centrifuge assembly facility at Karaj, and the heavy-water research complex at Khondab.

A fourth site, the enrichment plant at Natanz, was not included in the protocol, and Iranian officials have publicly insisted that the facility’s status falls outside the immediate post-ceasefire mandate. A senior Iranian official, speaking on condition of anonymity to describe the agency’s terms of reference, said access to Natanz would be “discussed in a later phase, on a different timeline, and not under the pressure of this week.”

“The agency’s task at these three sites is straightforward in concept and extraordinarily difficult in execution,” said Mark Hibbs, a senior fellow at the Carnegie Endowment for International Peace who has tracked the Iranian program for two decades. “Grossi is not there to make judgments about culpability or about future enrichment plans. He is there to take samples, count centrifuges, photograph damage and produce a baseline. Everything that comes after — sanctions sequencing, the suspension protocol, the question of whether the program has been set back two years or two months — depends on that baseline.”

The visit comes after weeks of diplomatic effort by the Islamabad mediation troika to secure Iranian agreement to inspections before the country’s parliament could legislate restrictions. The Majles, recalled from recess last week, has begun debating a bill that would condition all foreign inspections on prior Cabinet approval, and Iranian officials privately told mediators that the window for an inspection visit under existing authorities was narrow. A senior Pakistani diplomat involved in the Islamabad track described the timing as “a corridor we had to walk through this week.”

Grossi was scheduled to meet Wednesday afternoon with Eslami and senior Atomic Energy Organization technical staff, and on Thursday morning with Araghchi and President Masoud Pezeshkian. The inspection teams, divided into three groups, were expected to begin work at Karaj on Thursday, at Khondab on Friday and at Fordow on Sunday. Each site visit was projected to last two to three days, with sample analysis to be conducted at IAEA laboratories in Seibersdorf, Austria, and a preliminary report to the Board of Governors targeted for May 12.

A White House statement issued before dawn Washington time called the inspection mission “a necessary step toward a verifiable cessation of nuclear-weapons-related activity,” and said the United States would await the agency’s findings before commenting on what relief, if any, would accompany Iranian compliance. The statement, attributed to National Security Council spokesman Sean Parnell, did not mention sanctions sequencing directly, but a senior administration official described the inspection results as “the gate” through which any sequencing discussion would have to pass.

Israeli officials, who have insisted throughout the post-ceasefire period that they remain free to act unilaterally against any reconstituted Iranian nuclear capability, struck a notably reserved tone on the inspections. A statement from the Prime Minister’s Office in Jerusalem said Israel “welcomes any rigorous, independent and unhindered verification of Iranian nuclear sites,” and added that Jerusalem expected the agency’s access to be “complete in scope and uncompromising in standard.” Foreign Ministry director-general Dani Carmon, in Vienna for consultations with European partners, told Israeli army radio that the test would be “what Grossi reports, not what he says.”

Inside the inspection team, several technical specialists were drawn from the agency’s safeguards division and have prior experience with damage assessment at sites including Iraq’s Tuwaitha complex and Syria’s Al Kibar. Two engineers were specialists in centrifuge metallurgy, a discipline expected to be central to assessing how many of the roughly 1,800 advanced IR-6 machines Iran had installed at Fordow remained functional, recoverable or destroyed.

“You can bomb a centrifuge cascade, and you can rebuild a centrifuge cascade,” said Layla Hassan, a Beirut-based regional analyst. “What you cannot easily reconstitute is the institutional knowledge of the engineers who designed it. Grossi’s team will be looking, in part, at whether the people who built these cascades are still on payroll, are still in country, are still working. That is harder to verify than the count of standing machines, but it is at least as important.”

European officials, who have funded a portion of the inspection mission’s logistics, were watching the visit closely. EU High Representative Kaja Kallas, in Brussels, said the bloc had “full confidence in the agency’s professionalism” and that the European arms-control team deploying to the Strait of Hormuz this week would coordinate with IAEA inspectors as appropriate.

Russian and Chinese diplomats, who have long pressed for the lifting of pre-war sanctions in parallel with any verification regime, were less measured. Russian Permanent Representative to the IAEA Mikhail Ulyanov said in Vienna that the inspection mission “must not become an instrument of political pressure,” and called for a “balanced and reciprocal” approach to sanctions relief tied to verification milestones.

Grossi was scheduled to return to Vienna on April 30 and to brief the agency’s Board of Governors on May 12. Iranian officials said a fuller statement would follow Thursday’s meetings, and mediators in Islamabad indicated that the inspection findings would feed directly into a non-binding principles document still expected to circulate before the end of the month.