The threat has cast uncertainty over the opening of high-stakes negotiations aimed at turning a fragile ceasefire into a longer-term peace agreement.The warning came as senior US and Iranian officials gathered in Switzerland for the first round of talks aimed at building on a preliminary memorandum of understanding reached last week to end months of regional conflict.Posting on Truth Social as negotiations got underway, Trump said Iran must "immediately stop their highly paid proxies in Lebanon from causing trouble" "If they don’t, we’ll hit Iran very hard again, just like we did last week, only harder!!!" he wrote.Iran responded swiftly with chief negotiator Mohammad Bagher Ghalibaf warning the US to "be careful" with its language, saying Iran's armed forces were prepared to respond and insisting US threats had failed to alter Iran's position.The heightened rhetoric briefly fuelled speculation that the negotiations could unravel before substantive discussions had begun.Iranian state media reported Iran's delegation had left the venue in response to Trump's comments, with some outlets suggesting the talks had been suspended