Donald Trump has warned that Iran’s “whole civilisation will die tonight” if Tehran did not comply with his demands, as the world braced to see if the president would deliver on his latest threat to order the mass destruction of Iranian power plants and bridges in the absence of a deal by 8pm EDT (1am BST).

Iran’s Revolutionary Guards signalled they were also ready to escalate the war with a threat to retaliate “beyond the region” and “to deprive the US and its allies of oil and gas in the region for years”, suggesting Iran would target oil and gas production facilities in the Gulf and elsewhere, potentially sending the world into a recession.

The White House issued a statement on Tuesday insisting the US was not considering the use of a nuclear weapon after the vice-president, JD Vance, triggered concern with a warning that US forces had tools they “so far haven’t decided to use”.

But by threatening Iranian “civilization”, Trump appeared unwilling to dispel doubts he was prepared to commit serious war crimes by targeting the country’s population. On Sunday, he said US bombing would destroy all Iran’s power stations and bridges within fours hours of his deadline.

Late on Tuesday, Pope Leo described Trump’s threats as “truly unacceptable” and urged people across the world to contact their political leaders to call on them to bring the conflict to an end.

“Today as we all know there was this threat against all the people of Iran. This is truly unacceptable,” he said.

The pope added that attacks on civilian infrastructure were “against international law, but … also a sign of the hatred, the division, the destruction the human beings are capable of, and that we all want to work for peace”.

With Trump’s deadline looming, there was little sign of Pakistani-led peace efforts bearing fruit, with Iran unwilling to give up its main point of leverage, the near-total closure of the strait of Hormuz, the chokepoint for the flow of oil, gas and petrochemicals such as fertiliser from the Gulf, in return for a temporary ceasefire.

Hours before the deadline, Shehbaz Sharif, Pakistan’s prime minister, publicly requested that Trump delay his ultimatum to Iran by two weeks in order to “allow diplomacy to run its course”.

Sharif did not offer any specific updates on the negotiations, but said diplomatic efforts were “progressing steadily, strongly and powerfully, with the potential to lead to substantive results in near future”.

White House spokesperson Karoline Leavitt told Axios that Trump “had been made been aware of the proposal, and a response will come”.

Sharif also requested that Iran open the strait of Hormuz “as a goodwill gesture” and that “all warring parties” observe a two-week ceasefire. Reuters cited a senior Iranian official as saying that Tehran was reviewing the ceasefire proposal “positively”.

However, reports indicated explosions in Doha, Qatar, on Tuesday evening, as sirens were heard in Bahrain, where local residents have been requested to shelter in place, and interceptors were said to have engaged targets over the United Arab Emirates.

Mohammad Reza Aref, Iran’s first vice-president, said the country was ready for all possibilities as the deadline approached. “National security and infrastructure sustainability are the subject of our precise calculations,” he wrote on social media. “The government has finalised the necessary measures in detail for all scenarios. No threat is beyond our preparedness and intelligence.”

Earlier on X, Iran’s president, Masoud Pezeshkian, said: “More than 14 million proud Iranians have so far registered to sacrifice their lives to defend Iran. I too have been, am and will remain devoted to giving my life for Iran.”

Tehran has presented its own 10-point plan, insisting on long-term security guarantees, which Trump has rejected as “not good enough”.

After days of escalating threats, Trump posted a warning on social media Tuesday: “A whole civilization will die tonight, never to be brought back again. I don’t want that to happen, but it probably will.”

The president has set deadlines before and allowed them to pass over the five weeks of the conflict, but he insisted on Tuesday the ensuing hours would be “one of the most important moments in the long and complex history of the World” unless “something revolutionarily wonderful” happened, with “less radicalized minds” in Iran’s leadership.

Amir-Saeid Iravani, Iran’s representative at the UN, said that Trump’s threats constituted “incitement to war crimes – and potentially genocide”.

During a security council session on the strait of Hormuz, Iravani said: “Iran will not stand idle in the face of such egregious war crimes. It will exercise, without hesitation, its inherent right of self-defence and will take immediate and proportionate reciprocal measures.”

Through his spokesperson, the UN secretary-general, António Guterres, issued a reminder on Monday that attacking civilian infrastructure is banned under international law, but Trump declared on the same day he was “not at all” concerned about being called a war criminal.

Officers in the chain of command are obligated under US and international law not to carry out blatantly unlawful orders but it was unclear whether there was anyone left in Trump’s entourage willing to intervene to stop him.

In the hours before Trump’s deadline, Israel mounted its own attacks on Iran’s infrastructure. A rail bridge in the central 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 were reported in the same city after a substation and transmission lines were bombed. Bridges near Qom and Tabriz were also reportedly hit.

The US also struck 50 military targets on Iran’s Kharg Island, the home to its main oil export terminal, while Iran’s Revolutionary Guards said they had attacked Saudi Arabia’s Jubail petrochemical complex in retaliation for strikes on an Iranian petrochemical facility the night before.

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.

Iranian media reported on Tuesday that the 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 was produced, as well as a ballistic missile launch site in north-western Iran.

Israel’s military expressed regret on Tuesday for damage caused to a synagogue in Tehran, claiming it was “collateral damage” from a strike against a “senior military target”. Iranian media said the synagogue, serving the capital’s small Jewish population, had been destroyed.