US Vice President JD Vance arrived Sunday in Switzerland to help formally launch negotiations with Iranian leaders over curbing Tehran's nuclear programme and building out the fragile interim deal to end the war in Iran.
The framework was signed last week, and now top US and Iran negotiators are in a 60-day sprint to reach agreement on the technical details that hold massive implications for the world economy and global security.
Yet the first days of that two-month period were complicated by the heavy exchange of fire in Lebanon between Israel and the Iranian-backed militant group Hezbollah - and by the subsequent announcement by Iran's military that it had closed the Strait of Hormuz, the vital waterway that transits a fifth of the world's traded oil and natural gas.
Vance had originally been slated to be on the ground at the picturesque Bürgenstock resort near Lucerne on Friday, but his departure from the United States was delayed after fighting escalated in Lebanon and Iranian officials cancelled plans to attend the talks.
US Central Command disputed Iran's claim that it had once again shuttered the strait and said US forces continued to monitor the situation to ensure traffic continues to flow through the waterway. Vance has said that millions of barrels of oil have moved through the strait in recent days.
Vance departed the US just after Iranian state TV said Iran's negotiators had arrived in Switzerland. Tehran's negotiators include parliamentary speaker Mohammad Bagher Qalibaf and Foreign Minister Abbas Araghchi, along with central bank and oil officials.
The US vice president joins special envoy Steve Witkoff and Jared Kushner, President Donald Trump's son-in-law, who have already been on the ground to begin sifting through the technical details of the nuclear talks.
The talks between US and Iran will also include Pakistani Prime Minister Shehbaz Sharif and army chief Field Marshal Asim Munir, as well as Qatari mediators.
While Vance said he planned to be in Switzerland for just "a day or two," leaving much of the detailed negotiations to be spearheaded by Witkoff and Kushner, his role in the talks has heightened the scrutiny of the vice president at a time when he's actively considering a 2028 presidential campaign.
Trump and Vance have come under searing criticism from parts of their own party for the deal, with Republican hard-liners unfavourably likening it to a nuclear agreement signed by the Obama administration that Trump and the GOP have insisted did nothing to actually terminate Iran's nuclear programme.
The agreement signed by Trump and Iranian President Masoud Pezeshkian immediately allows Tehran to sell its oil freely and paves the way for Iran to tap into billions of dollars in assets that are currently frozen. It also calls for Iran to dilute its stockpile of highly enriched uranium, believed to be buried under nuclear sites that were targeted in US strikes last summer.
The agreement says commercial vessels can pass through the Strait of Hormuz for 60 days without a charge, but does not preclude future fees imposed by Iran.
Trump made his own threat on Saturday to levy US tolls on the strait if there is no deal with Iran in 60 days, insisting in a social media post that the money would be for "services rendered as the Guardian Angel to the countries of the Middle East."
Further complicating matters, neither Israel nor Hezbollah are signatories to the deal between the US and Iran, and Israeli Prime Minister Benjamin Netanyahu has vowed to keep his forces in southern Lebanon until any threat to Israel is eliminated. Hezbollah has refused to halt its attacks unless Israel commits to withdrawing from Lebanon.
Fighting between Israel and Hezbollah in the initial days after the agreement between the US and Iran killed 47 people in Lebanon, as well as four Israeli soldiers.
Israel vows to defend its forces in Lebanon
A halt to fighting in Lebanon was one of the conditions for starting US-Iranian talks on Tehran's nuclear programme and other issues. But Lebanese Civil Defence said 20 people had been killed by Israeli strikes in Lebanon on Saturday, hours after a truce took effect there.
Israel said it was responding to attacks from Hezbollah, while the Iran-backed militant group said it would not allow Israel "freedom of movement" in Lebanon. Israel says it is not party to the Iran-US deal and will keep its forces in the Lebanese territory it occupies.
A military statement said Israel was committed to the ceasefire but would continue to act against any threat to Israel or its forces.
Israeli broadcaster Channel 12 reported that the prime minister and defence minister had instructed the military to hold fire in Lebanon but that it would not withdraw from areas it had captured.
A poll by Israel's Hebrew University, shared with Reuters, found that some 92% of Israelis believe Iran benefited more from the joint Israeli-US military campaign than Israel and only some 8% think Israel emerged victorious. Almost 90% of Israelis said the goals of the war were not met and more than 70% do not believe Prime Minister Benjamin Netanyahu's claims that there were major achievements.
Lebanon's state news agency NNA said Israeli warplanes and drones had struck locations across southern Lebanon and the Bekaa Valley on Saturday, both Hezbollah strongholds.
An Israeli military official said Hezbollah fired more than 50 projectiles at Israeli forces in southern Lebanon overnight, and that Israel had attacked what it described as Hezbollah targets in response.
Lebanon's health ministry says 4,057 people have been killed in Israeli attacks since March 2, including medics, women and children, though it does not specify how many of the dead were combatants.
Israeli authorities say at least 32 soldiers and four civilians have been killed in fighting with Hezbollah.