Washington, April 8 -- President Donald Trump threatened Iran with civilisational destruction as the US attacked military targets on the country's key oil export hub, ramping up pressure on Tehran to reopen the Strait of Hormuz by his Tuesday morning (Tehran time) deadline or face massive strikes on critical infrastructure. Iran halted participation in ceasefire talks in response to Trump's social media post, according to a person familiar with the matter who asked not to be identified discussing private deliberations. Those discussions have been conducted through third-party channels, including Pakistan and Turkey. Mediators were scrambling to resuscitate negotiations ahead of the deadline, the person said. A senior White House official downplayed Iran's move and said that legitimate negotiations continue to take place. The lead-up to Trump's Tuesday 8 pm (US times) deadline has been marked by military escalation and increasingly bellicose threats from the US president. Earlier in the day, American forces struck sites on Kharg Island similar to those that were hit in a round of attacks last month, but didn't target energy infrastructure, according to US officials. "A whole civilization will die tonight, never to be brought back again. I don't want that to happen, but it probably will," Trump posted on social media. "Maybe something revolutionarily wonderful can happen, WHO KNOWS? We will find out tonight." Even as the US and Israel kept up attacks on infrastructure earlier on Tuesday, Trump's threat raised the specter of a massive new bombing campaign far exceeding anything they've carried out over the course of a campaign that began Feb. 28. Oil prices swung between losses and gains in yet another choppy session as investors tried to gauge whether energy infrastructure would come under attack ahead of Trump's deadline. Brent was trading near $109 a barrel while US crude for May traded above $115 a barrel. The US leader's latest ultimatum marks a critical juncture in the war that has killed more than 5,200 people, most of them in Iran and Lebanon, and seen energy facilities struck across the region. The president began issuing deadlines on March 21 to force Iran to reopen Hormuz, which carries roughly a fifth of seaborne oil shipments, and has repeatedly extended the timeline. He said Monday it's "highly unlikely" he'll do so again. Russia and China vetoed a United Nations Security Council resolution that would have encouraged efforts to revive shipping traffic in the strait, amid concerns that it would have tacitly condoned military action. Trump said during a news conference on Monday that freedom of navigation through Hormuz must be part of any deal. He has previously threatened to destroy Iranian power plants, bridges and other infrastructure as part of his ultimatum. The UN has warned that indiscriminate targeting of civilian infrastructure could constitute a war crime. Trump said he's "not at all" concerned about that potential outcome. Elsewhere, two people were killed in a US-Israel attack on a railway bridge near the Iranian city of Kashan on Tuesday, state-run Nour News reported. A synagogue in Tehran was destroyed overnight by what Iran said were Israeli air strikes. Footage in Iranian media showed Hebrew texts scattered in the debris. Israel is preparing for the possibility that fighting could continue for several more weeks, and on Tuesday told Iranians not to use their country's railway network until 9 p.m. local time - the type of warning it sometimes issues before attacks on civilian areas. Earlier, Iranian official Alireza Rahimi issued a video message calling on "all young people, athletes, artists, students and university students and their professors" to form human chains around power plants. President Masoud Pezeshkian posted on X that 14 million Iranians had answered campaigns urging people to volunteer to fight - and said he would join them - while a Revolutionary Guard general urged parents to send their children to man checkpoints....