Tehran (AFP) - Iran said it was once again closing the vital Strait of Hormuz on Saturday over Israeli attacks in Lebanon, as Iranian and US negotiators prepared to converge on Switzerland for talks on implementing a deal to end the Middle East war.

Follow-up negotiations had been planned in Switzerland on Friday, but were postponed at the last minute as Israel carried out a wave of deadly strikes in Lebanon after four of its soldiers were killed in combat.

The US announced a renewed ceasefire there on Friday afternoon – a stipulation under the deal it signed with Iran – but Israeli troops clashed with Hezbollah fighters and conducted strikes again on Saturday, with both sides accusing the other of violating the new truce.

Citing a US “breach of contract” and “the Zionist regime’s continuous and relentless violation of the ceasefire in southern Lebanon”, Iran’s central military command announced Saturday “that the Strait of Hormuz will be closed to vessel traffic”.

The Revolutionary Guards’ naval force warned vessels not to approach the waterway, “otherwise, their security will be jeopardised”.

The strait, an important conduit for oil and gas shipments, was blockaded by Iran for much of the war, sending shockwaves through global energy markets.

Tehran had agreed to reopen it under the preliminary accord signed this week by President Donald Trump and his Iranian counterpart Masoud Pezeshkian, and shipping traffic had started to pick back up in recent days.

The US military’s Central Command said after the announcement that its “forces remain present and vigilant to ensure all aspects of the agreement with Iran are adhered to”.

- Switzerland talks -

An Iranian delegation left for Switzerland on Saturday afternoon, state media reported, with foreign ministry spokesman Esmaeil Baqaei saying they would “demand implementation of the other party’s commitments” under the deal as soon as possible.

“Otherwise, the entire understanding will be in trouble,” he said, according to official news agency IRNA.

After postponing a planned trip the day before, US Vice President JD Vance told Fox News on Saturday that he too expected to travel to Switzerland for talks in “the next couple of days, but you know it’s always a delicate coordination dance”.

US negotiators Jared Kushner and Steve Witkoff were already in Switzerland handling “some of the technical elements” and had reported that “things are going well”, Vance added, just moments before the Iranian announcement about the Hormuz strait.

Mediator Pakistan – whose interior minister was reportedly in Iran on Saturday for meetings with officials – said “technical-level talks” were scheduled for Sunday.

The Swiss talks are meant to kick off a two-month period of negotiations to discuss outstanding issues not covered by the initial deal, notably Iran’s nuclear programme.

Switzerland’s foreign ministry confirmed unnamed foreign envoys there were “continuing their efforts to maintain the dialogue”, but declined to offer further details.

- Lebanon fighting -

Following Israel’s heavy strikes in Lebanon on Friday – which killed 83 people, according to health authorities – a US official announced a new ceasefire brokered by US and Qatari mediators.

But on Saturday an Israeli military official said it was conducting fresh attacks against Iran-backed Hezbollah, accusing it of having “launched more than 50 projectiles at Israeli forces in southern Lebanon” overnight.

Hezbollah in turn accused Israel of having carried out “under the cover of the ceasefire… an infiltration attempt towards the Ali Taher hills”, a strategic feature overlooking the city of Nabatieh, adding its fighters “confronted them with appropriate weapons”.

Lebanese state media reported Israeli air raids on around 20 locations Saturday, with the country’s civil defence agency saying 16 people were killed in the Nabatieh area.

Lebanon’s health ministry said seven more people were killed and 13 wounded in a strike on a village near Sidon, and reported that the overall death toll from the fighting had surpassed 4,000.

Hezbollah lawmaker Hassan Fadlallah said Saturday that his group retained “the full right to confront this enemy when it attacks us”.

An Israeli military official cited by public broadcaster Kan meanwhile described his country’s approach to the truce as being based on “fire being answered with fire”.

Israel’s US ambassador Yechiel Leiter maintained it was Hezbollah that broke the truce, adding Israel was “defending itself against terrorist attacks, as any self-respecting country would”.

But Hezbollah said Israel bore “full responsibility”.

Fadi Zayat, who had fled the southern Lebanon town of Tayr Debba, told AFP that “fear dominates” the atmosphere in the south.

“We returned to the village a few days ago, but our bags are ready to flee again,” the 53-year-old said.

Hezbollah pulled Lebanon into the wider Middle East conflict in early March when it fired rockets at Israel in retaliation for the killing of Iran’s supreme leader in US-Israeli strikes.

A previous ceasefire meant to take effect in Lebanon in April was never honoured, with each side justifying its attacks by the other’s alleged violations.

burs/smw/jfx