VIENNA — A joint technical committee convened at the International Atomic Energy Agency’s headquarters on Monday morning to translate the inspection annex of the Doha ceasefire extension into operating procedures, with negotiators racing to lock down access rules at three Iranian nuclear sites before the first on-site visit, tentatively penciled in for May 19.

The session, gaveled in at 9:42 a.m. local time by IAEA Director General Rafael Grossi, brought together inspectorate engineers, Iranian Atomic Energy Organization staff, and observers from the four governments seated on the technical review panel agreed in Doha on Friday: the United States, Germany, Pakistan and Saudi Arabia, the first occupant of the rotating Gulf seat. Israeli officials were not present in the room but were briefed throughout the day through a U.S. liaison cell, in keeping with the indirect-verification formula written into the extension.

“This is the unglamorous part of diplomacy and it is the part on which everything else depends,” Mr. Grossi told reporters in a brief corridor stop before the morning plenary closed to the press. “If we do not get the chain of custody right in this room, the political agreement that was signed in Doha last week will not survive its first contested sample.”

The technical team’s mandate, set out in a three-page tasking memo issued by Qatari and Pakistani co-chairs on Saturday night, covers four headings: scope of access at Natanz, Fordow and Isfahan; chain-of-custody for environmental samples and imagery; deconfliction protocols for inspector movement through Iranian airspace; and the formal mechanism by which Israel will receive unredacted summaries through Washington within 72 hours of each visit. A senior IAEA official, briefing a small group of reporters on background after the morning session, said all four were on the agenda for this week and that none had yet been closed.

Iran’s lead technical envoy, Behrouz Kamalvandi, arrived from Tehran on Sunday evening and met privately with Mr. Grossi for roughly 90 minutes before the formal opening. In remarks to Iranian state media on the tarmac at Vienna International Airport, Mr. Kamalvandi said his delegation had come “to implement, not to renegotiate,” and reiterated Tehran’s insistence that the inspection regime would apply only to the three sites struck during the war and not to the broader Iranian fuel cycle. He declined to comment on a question about whether Iran would accept short-notice visits, the most contentious of the unresolved protocol items.

The American delegation is led by Ambassador Laura Holt, the State Department’s principal deputy for nonproliferation, who flew to Vienna on Saturday from consultations in Riyadh. Ms. Holt told a small pool at the U.S. mission that the administration’s posture was “to make sure the verification works on its own terms, not to relitigate Doha.” She added that Washington would not block “reasonable Iranian sequencing concerns” so long as the substantive access envelope agreed Friday was preserved.

European officials present in Vienna described the mood inside the technical sessions as businesslike but tightly bounded. “There is no room here to test goodwill. There is only room to operationalize the text,” said one senior European diplomat, who was granted anonymity to describe a closed session. “Every word in the chain-of-custody section has a German engineer, an Iranian engineer and a Saudi observer reading it the same way. That is harder than it sounds.”

The committee’s most politically sensitive item is the protocol governing what the Doha text calls the “Israeli summary channel” — the redacted-then-unredacted pathway by which inspection findings travel from Vienna to Washington to Jerusalem. A draft technical schedule circulated late Sunday by Pakistani envoy Asim Iftikhar proposes that summaries be hand-delivered by a U.S. nonproliferation officer at the U.S. embassy in Jerusalem rather than transmitted electronically, a measure intended to limit the digital footprint that Iranian negotiators raised as a concern during the final 48 hours of the Doha talks. The summaries would arrive in a sealed pouch within 72 hours of each visit and be opened in the presence of an IAEA observer, two officials briefed on the draft said.

Israeli Prime Minister Benjamin Netanyahu, briefed Sunday evening at his Jerusalem residence by national security adviser Tzachi Hanegbi and U.S. ambassador Mike Huckabee, told members of his security cabinet that he would await the first inspection cycle before judging the regime, according to a readout shared by two coalition officials. The same officials said the prime minister had instructed his team not to leak operational details and had reiterated that any “material reconstitution” of Iranian enrichment beyond declared thresholds would warrant a renewed military response, a position the United States neither endorsed nor contradicted in its own briefing notes circulated Monday.

The Vienna session opens against a backdrop of domestic political churn in both capitals. Mr. Netanyahu is operating with a 61-seat working Knesset majority following the resignation of two far-right ministers a week ago and is in continuing coalition talks with the centrist National Unity bloc led by Benny Gantz. In Tehran, President Masoud Pezeshkian’s government is contending with renewed bazaar protests over the cost of staples and a parliamentary inquiry into the Supreme National Security Council’s wartime conduct. Western diplomats said both governments had a near-term political interest in a smooth opening week.

“Neither side can afford a procedural fight that becomes a headline,” said Layla Hassan, a Beirut-based regional analyst at the Levant Policy Forum, in a telephone interview. “The political weather in both Jerusalem and Tehran is uncertain enough that a clean Vienna would be valuable to both prime ministers, even if neither will say so out loud.”

The IAEA itself is operating with stretched resources. The agency in late April requested a 24 million euro supplemental from its board of governors to cover the inspection workload through the end of the year, and is recruiting additional safeguards inspectors with experience in centrifuge facilities, a specialization in short supply since the 2015 nuclear deal lapsed. Mr. Grossi told reporters Monday that the agency had identified 38 qualified candidates and expected to deploy the first tranche before the May 19 visit.

Outside the headquarters building, a small group of protesters representing families of Iranian dissidents and Israeli reservists held parallel demonstrations, separated by Austrian police. Inside, the technical sessions were expected to run through Friday, with a brief joint statement anticipated at the close of business each day. Officials in Vienna said additional procedural deliverables, including the final wording of the deconfliction protocol governing inspector movement through Iranian airspace, would be released as they were agreed.