Diplomacy between the United States and Iran over the future of Tehran's nuclear program has hit a new snag -- not over uranium enrichment or sanctions, but over the simple matter ofwhento meet.

As US President Donald Trump insists the next round of talks is set for June 12, Iranian Foreign Ministry spokesman Esmail Baqaei maintains that negotiations will resume on June 15 in Muscat. Oman, which is mediating the talks, has not weighed in.

The scheduling dispute comes as Iran's chief negotiator, Foreign Minister Abbas Araqchi, is slated to be in Norway on June 12 for the Oslo Forum, making a session that day with the US unlikely, but not impossible. Oman's Foreign Minister Badr Albusaidi will also be in Oslo, so if White House envoy and nuclear negotiator Steve Witkoff travels to Norway, a meeting could take place.

Despite the calendar confusion, the stakes are clear: The sixth round of talks is shaping up to be a defining moment. Iran has formally rejected Washington's proposal for a deal, calling it "unacceptable" and lacking in key areas, especially the removal of economic sanctions and recognition of Iran's right to enrich uranium on its own soil.

Iran's Counterproposal On Enrichment

Tehran says it will soon submit acounterproposalvia Oman, a plan it describes as "reasonable, logical, and balanced" and which it urges Washington to take seriously.

While Iran has kept the details of its counteroffer under wraps, Deputy Foreign Minister Majid Takht-Ravanchi says it's not a lengthy document but a "rational" proposal that "can't be dismissed with a simple 'no.'"

He describes it as a solid and acceptable basis for further discussion.

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Iran's counterproposal is expected to insist on the right to continue uranium enrichment -- a non-negotiable point for Tehran -- and demand effective and verifiable sanctions relief before any Iranian concessions.

Trump and other US officials, for their part, remain firm that any deal must see Iran halt enrichment, a position Iran's Supreme Leader Ayatollah Ali Khamenei has flatly rejected as "100 percent contrary" to national interests.

Specter Of IAEA Resolution

This is all unfolding as the International Atomic Energy Agency (IAEA) Board of Governors meets in Vienna for its quarterly session, a gathering dominated by the Iran file.

The IAEA's latest comprehensive report, released on May 31, concluded that Iran has failed to provide credible answers about undeclared nuclear material and activities at several sites, and that its cooperation with inspectors has been "less than satisfactory."

Iran's ambassador to the IAEA Reza Najafi (right) and Massimo Aparo, IAEA head of the department of safeguards, speak upon arrival for the IAEA's Board of Governors meeting in Vienna on June 9.

The United States and its European allies -- Britain, France, Germany, also known as the E3 -- are now pushing a resolution that would formally declare Iran in noncompliance with its safeguards obligations for the first time in two decades.

If adopted, the resolution would not immediately escalate the matter to the UN Security Council, but it would give Iran a window to address the outstanding concerns. It would be a major step toward opening the door to the return of UN sanctions if Iran fails to comply.

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Meanwhile, Iran hasthreatenedto retaliate if the resolution is adopted, teasing that it may expand its nuclear program, including installing thousands of advanced centrifuges.

The "snapback" of UN sanctions is a provision under the now-defunct 2015 nuclear deal and the E3 wants to use it before it expires in October.

Whether the resolution is adopted could shape the tone of the next round of nuclear talks.

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Iranian TV Alleges Massive Spy Operation Targeting Israeli Nuclear Sites

Adding to the volatility, Iran's Intelligence Ministry claimed over the weekend that Tehran has obtained a"treasure trove" of sensitive Israeli documents, including material on Israel's nuclear program and defense capabilities.

With Israel preparing to strike Iranian nuclear sites if the negotiations with the United States fail, the Supreme National Security Council said the alleged intelligence breach will allow Iran to retaliate to a potential attack "immediately" by targeting Israel's "secret nuclear facilities."

For now, the world is left waiting -- not just for the substance of a deal, but for the negotiators to even settle on a time and place to argue.