Although the US and Iran had agreed to a 60-day ceasefire while negotiations take place, Tehran’s Islamic Revolutionary Guard Corps on Saturday declared the Strait of Hormuz shut, though the US military said commercial vessels had continued operating in the waterway. Those developments could complicate talks in which both sides want to advance an interim deal brokered by Pakistan and signed on Wednesday by Presidents Donald Trump and Masoud Pezeshkian to end the almost four-month war. Pointing to what it called Israeli “crimes” in Lebanon that violated US commitments to a ceasefire, the Revolutionary Guards warned ships would be at risk if they approached the Strait, a vital conduit for global oil and gas supplies. But US Central Command said 55 merchant ships transited the strait on Saturday with more than 17 million barrels of oil bound for global markets.
Tensions rose ahead of the talks after Iran’s Islamic Revolutionary Guard Corps (IRGC) and military officials announced that the Strait of Hormuz had been closed in response to what Tehran described as Israeli violations of ceasefire commitments in Lebanon.
Iranian officials argued that the interim agreement required a halt to fighting on all fronts, including Lebanon, and accused Washington of failing to ensure Israeli compliance.
The United States quickly challenged the claim.
“Iran does not control the Strait of Hormuz,” US Central Command spokesperson Capt. Tim Hawkins said, adding that commercial shipping continued to move through the waterway.
According to Central Command, 55 merchant vessels carrying more than 17 million barrels of oil transited the strait on Saturday. US officials said military forces would continue monitoring the route and ensuring freedom of navigation.
The Strait of Hormuz is one of the world’s most important energy corridors, handling a significant share of global oil and liquefied natural gas exports.
Trump sought to reassure markets, saying passage through the strait would remain toll-free during the 60-day ceasefire period. However, he also suggested the United States could impose future transit fees if negotiations fail, describing them as payment for US security protection in the region.
Iranian state media reported that a senior delegation led by parliamentary Speaker Mohammad Baqer Qalibaf arrived in Switzerland ahead of the talks. The delegation includes Foreign Minister Abbas Araqchi as well as senior security, central bank and energy officials.
US Vice President JD Vance arrived in Switzerland on Sunday landing at Emmen Air Base at 5:59 am (0359 GMT), according to his spokesperson.
Pakistan’s Prime Minister Shehbaz Sharif and Army Chief Field Marshal Asim Munir, whose country played a central mediating role in securing the interim agreement, also traveled to Switzerland. Qatari mediators are expected to participate in the discussions.
Vance expressed optimism before departing.
“I think we’re going to hopefully make progress on the nuclear issue and make progress on the Lebanon ceasefire issue,” he said, adding that talks could last several days.
Iranian Foreign Ministry spokesman Esmaeil Baghaei said Tehran would seek concrete implementation of commitments already made, warning that failure to do so could jeopardize the broader agreement.
The situation in Lebanon remains the most immediate challenge facing negotiators.
Despite efforts to establish a ceasefire, violence continued over the weekend. Lebanese authorities reported at least 16 deaths from Israeli strikes on Saturday, while other reports put the toll at 20.
Israel said it was responding to attacks launched by Hezbollah, which in turn said it would not permit Israel “freedom of movement” in Lebanese territory.
An Israeli military official said Hezbollah fired more than 50 projectiles at Israeli forces overnight, prompting retaliatory strikes against what Israel described as Hezbollah targets.
Israeli officials indicated they had received updated political directives to halt offensive operations but would continue acting against perceived threats. Prime Minister Benjamin Netanyahu has repeatedly said Israeli forces will remain in parts of southern Lebanon until security concerns are addressed.
Neither Israel nor Hezbollah is a signatory to the US-Iran agreement, complicating efforts to secure a durable regional ceasefire.
Lebanon’s health ministry says more than 4,000 people have been killed since fighting escalated earlier this year, while Israeli authorities report dozens of soldiers and civilians have also died.
The Swiss talks are expected to focus on implementing the ceasefire, preventing further escalation in Lebanon, and negotiating terms for a longer-term agreement on Iran’s nuclear activities.
The interim accord also provides for the easing of some restrictions on Iran’s economy, including allowing Tehran to resume oil exports and regain access to frozen assets.
While both Washington and Tehran have expressed cautious optimism, the dispute over the Strait of Hormuz and continuing violence in Lebanon underscore the challenges negotiators face as they seek to convert the temporary truce into a lasting agreement.