US-Iranian negotiations in Switzerland suffered an abrupt interruption on Sunday after the Iranian delegation suspended its participation in protest at threats issued by President Donald Trump, even as Vice President JD Vance described the early hours of the talks as having produced “great progress.” The high-level meeting, convened at a resort near Lake Lucerne with Qatar and Pakistan acting as mediators, was intended to advance a 60-day framework for a comprehensive peace and nuclear agreement. Iranian news agencies reported that the delegation left the venue following Trump’s warnings, though US officials maintained that the discussions had not been formally terminated.

Viewed from Washington, the administration sought to use the summit to build momentum toward normalisation. Vance told reporters that the president wanted to “turn over a new leaf” in relations with Iran, and US officials signalled a willingness to unfreeze some $6 billion in Iranian funds held in Qatar in exchange for access by international inspectors to Iran’s nuclear facilities. Hours later, however, Trump posted online that Iran must immediately halt its “proxies” in Lebanon or face renewed strikes “harder” than those launched earlier. The White House also contested Iran’s claim to have again closed the Strait of Hormuz, insisting that commercial traffic was flowing under US Navy overwatch.

Tehran’s position, as articulated by President Masoud Pezeshkian and foreign ministry spokesman Esmail Baghaei, made any substantive final agreement conditional on a durable ceasefire in Lebanon. Iran reaffirmed its right to uranium enrichment while offering to provide written assurances against nuclear weapons development. The Iranian state news agency IRNA quoted officials stating that without an end to Israeli operations against Hezbollah, the Strait of Hormuz would remain shut and the negotiating phase of a final accord could not begin. This linkage placed the talks at immediate risk, given the continued fighting in southern Lebanon despite a ceasefire that is part of the earlier memorandum of understanding.

Mediators in Doha and Islamabad acknowledged the fragility of the process. Qatar’s foreign ministry had expressed hope that the technical and expert working groups would craft a lasting agreement covering all points of the memorandum, but the walkout froze those channels. The next steps remain uncertain: while Vance spoke of expecting “additional progress,” the political prerequisites set by both capitals leave the 60-day timeline under severe strain. For now, the dossier hangs on whether quiet diplomacy can bridge the gap between US military pressure and Iran’s demand for an immediate cessation of hostilities on its Lebanese flank.