Donald Trump warned that “a whole civilization will die tonight” if Tehran does not accept his demands, amid a wave of bombing as Israel told Iranians their lives would be at risk if they used the country’s railways.

A rail bridge in the central Iranian city of Kashan was one of the first reported bombed on Tuesday by Iranian state media, with two people reportedly killed as Israel’s military said it had launched “a wide-scale wave of strikes targeting dozens of infrastructure sites”.

A bridge over a railway line near Karaj, to the north-west of Tehran, was hit, according to Iranian media, and power outages reported in the same city after a substation and transmission lines were bombed. Bridges near Qom and Tabriz were reportedly hit.

The US also struck 50 military targets on Iran’s Kharg Island, the home to its main oil export terminal, as attacks on Iran escalated markedly in advance of an 8pm ET deadline set by the US president.

“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 Monday morning, before expressing hope that “less radicalised minds” would take over the country.

The extraordinary threats came hours before an ultimatum set by the US president expires at 8pm ET on Tuesday – 4.30am on Wednesday in Iran (1am UK time) – in an attempt to force major concessions from Iran.

Trump had repeatedly said the US was prepared to bomb Iran’s power plants and bridges in a concentrated attack on the country’s civil infrastructure if Tehran did not reopen the strait of Hormuz and abandon any effort to make nuclear weapons, though it appears some of the attacks may have already begun.

The prospect of bombing Iran’s infrastructure has been condemned by lawyers and experts as a probable war crime because its impact on civilians would be disproportionate to whatever notional military advantage was gained, a conclusion that has been dismissed by the Trump administration.

Israel’s military, writing in Farsi on social media, said on Tuesday morning that “from this moment” – 8.50am Iran time – until 9pm, Iranians should refrain from “travelling by train throughout Iran” for the sake of their own security.

“Your presence on trains and near railway lines endangers your life,” the statement continued in a clear warning that stations and tracks normally used by civilians would be bombed on Tuesday.

Iran on Monday rejected a proposal to implement an immediate ceasefire followed by peace negotiations brokered by Pakistan, Egypt and Turkey, arguing that it wanted a permanent end to the war. It issued a 10-point counterproposal, which Trump acknowledged but said was “not good enough”.

Negotiations continued on Tuesday morning, though there were few clear developments. On X, Iran’s president, Masoud Pezeshkian, said: “Over 14 million proud Iranians have, up to this moment, declared their readiness to sacrifice their lives in defense of Iran. I too have been, am, and will be a sacrificer for Iran.”

One Iranian source told Reuters that Iran also wanted compensation paid for damages and to be left in control of the strait, allowing it to impose fees on ships that use it, a condition that would be unacceptable to the US.

On Monday, Pete Hegseth, the US secretary of defence, said that “today will be the largest volume of strikes” on Iran and that attacks on Tuesday would be “even more than today”.

Iranian media reported on Tuesday that Khorramabad airport, in western Iran, had been attacked, and Israel said it had conducted another wave of strikes on Tehran overnight. Israel’s military said it had bombed a petrochemical facility in Shiraz, where it said nitric acid used to make explosives is produced, as well as a ballistic missile launch site in north-western Iran.

Iranian media also reported that a synagogue in Tehran was destroyed in the bombing, though Israel said it does not target synagogues.

US officials told Fox News and the Wall Street Journal that B-2 stealth bombers had dropped 30,000lb “bunker buster” bombs on an Islamic Revolutionary Guard Corps compound in Tehran on Saturday. The bombs were GBU-57 munitions, the type used in last June’s attack by the US on Iran’s underground nuclear facility at Fordow.

Israeli media reported that Benjamin Netanyahu told members of the country’s security cabinet on Sunday that the war against Hezbollah in Lebanon would continue regardless of what happened in the negotiations between the US and Iran. There was, the prime minister said, a “separation of theatres”.

An attack on Saudi Arabia had hit a petrochemical complex in a sprawling industrial area in the eastern city of Jubail and workers at the site were evacuated.

Sirens were repeatedly sounded in Israel as missile attacks continued. Five impacts were reported in the Tel Aviv area as Israel said Iran had fired ballistic missiles with cluster warheads, but no casualties were immediately reported.

The price of Brent crude oil increased marginally to just above $110 (£83) a barrel in morning trading.