A new round of negotiations over the Middle East war was set to kick off on Sunday as Iranian negotiators and US Vice-President J.D. Vance arrived in the Swiss host city, even as Tehran said it was closing the Strait of Hormuz again over Israeli attacks in Lebanon.

Before boarding his flight to Europe, Vance told reporters he hoped to “make progress on the nuclear issue, make progress on the Lebanon ceasefire issue. Those are the two big things that I think we’re going to be focused on”.

Follow-up talks had been planned in Switzerland on Friday but were postponed at the last minute after Israel launched deadly strikes in Lebanon following the deaths of four of its soldiers in combat.

Washington announced a renewed ceasefire there later on Friday – a condition of its preliminary agreement with Iran – but Israeli troops clashed again with Hezbollah fighters on Saturday, with each side accusing the other of breaking the 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 said “the Strait of Hormuz will be closed to vessel traffic”.

Hormuz, a key conduit for oil and gas shipments, was blockaded by Iran for much of the war, sending shock waves through global energy markets.