Iran has said it is closing the strait of Hormuz after waves of Israeli strikes in Lebanon in a move that threatens to derail the fragile interim peace deal with the US, signed just days ago.

The Islamic Revolutionary Guard Corps warned ships not to approach the strategic waterway, which before the war carried a fifth of global oil and liquid gas supplies, citing what it called Israeli crimes in Lebanon and a US violation of ⁠commitments to establish a ceasefire there.

It was unclear if the threat had been carried out, or if it would jeopardise talks in Switzerland scheduled for Sunday that were supposed to start the process of turning the current interim agreement between the US and Iran signed this week into a more detailed deal covering Iran’s nuclear programme.

There was no immediate reaction from Washington to the news of the possible closure of the strait, which Iran is required to keep open under the new deal.

Earlier on Saturday, JD Vance, the US vice-president, told Fox News he expected to travel to Switzerland in “the next couple of days” to take part in negotiations. Pakistan, the key mediator, said the talks would go ahead and reports from Tehran suggested that a delegation of top officials had left Iran to participate in the negotiations.

The continuing hostilities in Lebanon between Hezbollah, which has close ties to Iran, and Israel have emerged as the main challenge to the new deal to end the war in the Gulf.

Israeli strikes on southern Lebanon on Saturday killed at least 16 people, local authorities said, despite reports of a renewed ceasefire aiming to end the continuing clashes.

Lebanon’s civil defence agency said its personnel transported “16 dead and 12 wounded” to hospital, adding that they had been working “since the early morning hours” in the Nabatieh district.

The interim agreement calls for a cessation of hostilities on all fronts, including Lebanon. It has been fiercely criticised by Israeli ministers, officials and commentators, who argue that it stops Israel countering threats posed by Hezbollah.

The Israeli military said it was striking Hezbollah targets in response to overnight projectile launches from the Lebanese militant organisation.

Violence flared on Friday after four Israeli soldiers including a senior officer were killed when a tank was hit by Hezbollah, which said the strike had come after Israel broke a previous ceasefire agreement by advancing.

The Israeli attacks that followed killed 83 people, local authorities said, across southern Lebanon and the Bekaa valley.

The exact status of the new ceasefire reported to have come into effect locally on Friday evening was unclear. In public statements, Hezbollah has said it will abide by a ceasefire if Israel does, but has not said a ceasefire is actually in place.

Hassan Fadlallah, a Hezbollah parliamentarian in Lebanon, said his group had the right to respond to Israeli attacks.

“There is talk of a ceasefire. For us, what concerns us is that the enemy fully … doesn’t attempt to attack our country and villages or seek to occupy any new position,” he said in a statement.

The most recent round of war between Hezbollah and Israel began days after the US and Israel launched strikes on Iran on 28 February, with Hezbollah firing rockets and drones at civilian communities in northern Israel, and Israel seizing and occupying large swathes of southern Lebanon to establish a “buffer zone”.

The continuing violence and diplomatic back-and-forth over the planned talks between Iran and the US have fuelled scepticism that a definitive end can be found to a regional war that has killed at least ‌7,000 people, sent energy prices soaring and threatened global economic chaos.

The interim US-Iran agreement signed this week called for the US to lift its naval blockade in return for the reopening of the strait of Hormuz, which was closed to most shipping by Tehran shortly after the beginning of the conflict.

Neither Israel nor Hezbollah are signatories to the deal, which calls for a halt to military operations in Lebanon and for the country’s sovereignty to be respected.

Benjamin Netanyahu, Israel’s prime minister, has vowed to keep Israeli 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, which Iran says is also a condition of the deal.

Despite the violence in Lebanon, Vance said he was confident the ceasefire agreed in Washington’s 14-point deal with Tehran would hold, and that he had seen no evidence that ⁠the strait was closed.

“I expect that I will leave some time in the next couple of days, but you know it’s always a delicate coordination dance and the diplomatic protocols,” Vance said. He added that the US negotiators Jared ​Kushner and Steve Witkoff had been in Switzerland “for a few hours, dealing with some of the technical elements ‌of this negotiation”.

Iran’s foreign ministry spokesperson, Esmail Baghaei, however, signalled that little progress would be made until Iran was convinced the US was fulfilling its commitments under the deal.

“This trip is therefore about demanding that the other side fulfil its obligations,” Baghaei said.

The interim deal gives negotiators 60 days to come up with a nuclear agreement, but that can be extended. Many observers warn that it will be very hard to reach an agreement on such a complex issue within two months. The 2015 nuclear deal, which the US president, Donald Trump, scrapped during his first term, took more than 18 months to negotiate.