US President Donald Trump warned "a whole civilization will die" in Iran if the country does not heed his midnight cutoff to open the Strait of Hormuz, as Tehran reported US-Israeli attacks on its infrastructure were already underway.
Speaking in Budapest, Vice President JD Vance said the United States has "tools in our toolkit that we so far haven't decided to use" against Iran, without explaining further.
Iran's Revolutionary Guards warned they would deprive the United States and its allies of oil and gas if Washington crossed Tehran's "red lines".
The statements come as Iran reported that the United States and Israel had begun attacking key infrastructure, with Israeli Prime Minister Benjamin Netanyahu confirming attacks on railways and bridges and saying they were "used by the Revolutionary Guards".
Trump had initially vowed to carry out the "complete demolition" of Iran's critical infrastructure, particularly bridges and power plants, only if a deal was not reached.
But hours before the deadline, the Israeli military said it had already completed a broad wave of strikes targeting "infrastructure sites" across Iran.
Writing on Truth Social, Trump elevated his ultimatum for Iran, stating that "a whole civilization will die tonight, never to be brought back again. I don't want that to happen, but it probably will", if the country does not heed his call for a deal.
It was not initially clear exactly what he meant or by what means he intended to carry out the threat.
Infrastructure attacks reported by Iranian authorities included a US-Israeli strike on a bridge outside the city of Qom and another on a rail bridge in central Iran that killed two people.
Regional authorities also said a US-Israeli strike shut down a key highway in northern Iran connecting the city of Tabriz with Tehran.
The Mizan news agency additionally reported a strike on railway tracks in Karaj, outside Tehran.
University student Metanat, whose classmate was killed two weeks ago in an attack, told AFP that she was "terrified and so should everyone else in the country be".
The 27-year-old, who declined to give her last name, said as far as Trump's ultimatums were concerned, "some people think they are a joke", but "death is not a joke".
The Iranian military has previously dismissed what it called Trump's "arrogant rhetoric and baseless threats", saying they would not hinder its operations.
Alireza Rahimi, Secretary of the Supreme Council of Youth and Adolescents of Iran, called on young people to form human chains around power plants across the country.
On Tuesday the Israeli military told Iranians to avoid taking trains until 1730 GMT, and train travel to and from Iran's second city of Mashhad was cancelled until further notice.
In the Gulf, the King Fahd Bridge, a major artery connecting Saudi Arabia and Bahrain, was temporarily closed as a precaution amid fears of retaliatory strikes by Iran.
Strikes were also reported on Kharg island, a critical hub for the Iranian oil industry, according to Iran's Mehr news agency, although US media said the attacks were against military targets.
Earlier in the day a series of explosions was heard across Tehran, and Iranian media reported that 18 people, including two children, were killed in strikes in Alborz province neighbouring the capital.
US-Israeli strikes also "completely destroyed" the capital's Rafi-Nia synagogue, local media reported.
Overnight, attacks on Saudi Arabia hit a petrochemical complex in a sprawling industrial area in the eastern city of Jubail, a witness who requested anonymity told AFP, hours after similar installations in Iran were struck.
The Israeli military meanwhile said it had completed deployment of ground troops along a "defence line" in southern Lebanon, where it is fighting Iran-backed Hizbollah.
Both Trump and Iran have said a proposal touted by international mediators for a 45-day ceasefire is not yet ready.
Trump had said earlier that the plan, which is being mediated by Pakistan, Egypt and Turkey, was a "significant proposal", but he later went on to say it was not good enough.
Iranian state media quoted officials as saying that Tehran too "has rejected a ceasefire and insists on the need for a definitive end to the conflict".
On the diplomatic front, the UN Security Council is set to vote Tuesday on a watered-down resolution addressing Iran's threats to the strait, diplomatic sources told AFP, after more robust earlier drafts were derailed by the possibility of vetoes.
Iran has effectively blocked the waterway -- through which a fifth of the world's oil normally flows -- since the start of the war on February 28, driving up global energy prices.
Agence France-Presse
